We live in an age where information accumulates at a mind boggling rate and some of us have plenty of digital memories, information, and all that it would be a shame if all that poofed and went away. Being properly prepared for such an event requires making copies of your data (called backups). This guide will go over the basics of backing up and as an example, how I take care of backing up what's important to me.   1. What is backing up? Backing up is making copies of your data in the event that if the primary storage drive your data resides in goes bad, such as if there's data corruption or the drive dies, you have a way to bring it back. Note however that simply copying data is not backing up, depending on how it's done and where it lives.   2. The 3-2-1 Rule for backing up files
This is more of a guideline, but a good one because it's simple and provides coverage for a wide variety of issues you could possibly encounter with data loss. The 3-2-1 rule breaks down into this: Make at least 3 copies of data.
While having two is sufficient, having three or more increases copies the survivability of your data greatly.
  Have your data on at least two different "solutions"
By solution, I mean where the data lives and who's in charge of managing it if you're going with some software to manage it. Hardware wise, choose at least two physically different drives or media. This can be something like an external hard drive, some DVDs, or a thumb disk. If you're going with software to manage it, choose two different providers if you can. For example, if "Cool Backup Company" provides a local and cloud storage solution, don't count on it for both and find another company for the local or cloud storage solution

Note: RAID is not a backup solution because in the naive sense, RAID will copy the data as-is. So if the data gets corrupted and there's no error correction to catch this on the RAID side, the RAID system will keep the corruption.
  Have a copy of your data on at least one place offsite.
What if you had five copies spread out on different drives, but they were in the same house and the house burned down? Now you have nothing. Copies of your data should exist on at least one place offsite, be it with a trusted person, a safety deposit box, or in the cloud. In the most simplest form of following the 3-2-1 rule is that one copy of the data lives on the computer you use, another copy lives on an external hard drive, and the last copy lives on cloud storage system like Dropbox. You have three copies, at least two of which are physically separated, and at least one of those copies is offsite.
3. Choose what you want to backup
The easy answer would be "Everything!", but sometimes that's not doable. In my case, literally everything in my name including my documents, pictures, music, videos, and applications that I can keep would easily eat up over 6TB. Pare everything down to minimize the cost and requirements for your backup solution. You don't have to get Spartan, but at least find out what's not necessary to back up. For example, don't back up application installers unless you cannot download it from the internet. By the time you may actually need to reinstall the application, it's outdated, requiring you to download the up-to-date version anyway. Another one is don't backup things like temporary folders or where Windows is installed (there's a special process for backing up a Windows install).   4. Choosing the method of backing up @Ryan_Vickers made an excellent topic covering this, so go read that! But to summarize: Get an external hard drive (i.e. making a local copy) Use an always-syncing cloud storage method Use an occasional syncing cloud storage method   5. Choosing the hardware for a local copy
It's good to have a local backup copy of your files, since accessing them on the internet isn't always reliable and is always slower than having it right there. But you'll have to find the hardware to store it on! If this is your first time backing up, you’ll have to consider the capacity of your storage media. A good idea is to get more space than you currently need so you can have room to grow. As a rule of thumb, aim for a total capacity of at least 1.5 times the amount of stuff you want to store
For large capacities, getting a hard drive would seem like the obvious choice since they're relatively cheap for the amount of space you can get. However, being mechanical, they bring their own issues. For reliability, I do recommend getting NAS grade drives. However, I've used cheap "green" drives as backup drives before without a problem.
If your data isn't as large, you could opt for optical media. Keep in mind that recordable optical media usually uses some kind of dye which can degrade over the years if storage conditions aren't that great. While this was a major problem in the past, most decent optical media can last at least 10 years if kept in a cool dry place. If you're still keen on using optical media for longer term storage, you may want to get what's called a "gold archival grade" disc, but they do get pricey. (at the time of this writing, Amazon has a spindle of 50 for $80)   Flash-based storage can also be something to consider, but keep in mind that their offline storage life is not as good as hard drives. (Note about offline storage life is described in section 7)   6. Choosing the Software While I can’t recommend software specifically for backing up, as I have my own way and everyone's different, there are a few questions you should answer when choosing one so you can narrow down the features you want: How do you want access to it when you need it?
Some backup tools store files in a way that you can’t access them directly, or you need to restore the backup before you can access them. This is something to consider if you want to access your backup like regular storage.
  Do you want file history?
The way file history works is on the next backup, if the file has changed in any way, the backup will store the current copy, but have a way for the previous version to be accessible. Chances are software that does this won’t store an exact copy of the file, but the differences to save space. For example, if you modified a 10MB file to add another 2MB, the backup software will only store the 2MB difference, rather than store 12MB on top of the 10MB original file
  Do you want the process to be automated?
Automated in not just press a button and go, but also in a way that your computer will automatically schedule a backup session and run its course. The only downside is the backup itself is automatic, you have to make sure the backup media is readily available. User friendly software should remind you to make it available or remind you a backup is approaching.
Price is also a factor, but that comes with the territory. However, there are lots of free tools available and most modern OSes come with a basic one.
The most important thing however, is that you trust whoever is doing your backup solution to be around. Nothing's worse than going with a backup solution, only to find out that they no longer exist a year later and either your data is gone, or you have no means of accessing it.
7. After Backing Up, Make Sure It’s Still Good Once in A While
Your backup is no good if you can't access it, you find errors in it, or worse, the media died at some time. For local backup solutions, all storage hardware has something called cold storage life. This means that if the storage is powered off for an extended period of time, it may start to degrade. However this degradation process is very slow and very small, amounting to a bit flip. For hard drives, cold storage life is about a year. For flash memory, it's less, though I'm not sure how less. The reason flash memory is less is that flash memory acts like a very slow discharging capacitor. Optical media will degrade pretty much right from manufacturing.   Rather than waiting near the offline shelf life, it’s good to take out your backup media and “exercise it” so to speak. Once a month is good enough and you should update your backup during this time too. So after making your backup, do the following: Run a file system integrity check. On Windows you can right click on the drive, select “Properties”, go to the “Tools” tab, and press the “Check” button. On Mac OS X, use Spotlight to search for “Disk Utility.” You can also use terminal and run “fsck” as root. On Linux, run “fsck”, or your utility of choice. Review your really important files to make sure they’re not corrupted. You don’t have to go through all of them, but it’s a good idea to go through some of them. If you’re using a hard drive or even an SSD, you can also check the overall health of the drive by getting its SMART data. Crystal Disk Info is a tool that can display this data. Wikipedia has a list of values you should be mindful of if the hard drive is starting to die. 8. How I Do Backups
These are the requirements I have for backups. They’re sort of vague, but it’s a start I want a lot of control over the process. There are some things I don't want to back up, while there are other things I do. Or that I want them to be backed up in some places but not others. Because of that, I need to be able to control what gets backed up and where. I want to be able to access them readily, unless it’s going in a “store and forget” kind of place. I don't like the idea of having my backups in a "backup folder" that I can't access for some reason without the utility. Cloud storage is the exception. As mentioned earlier, I have copies of all my important stuff on several different storage devices/media. An external drive next to my computer. This is what I use for my “cold storage” backup, or the disk I keep offline most of the time. A NAS box. NAS if you don’t know is short for Network Attached Storage. This can be a self-contained computer or a portable hard drive with networking capabilities. It’s used for three things: a “hot storage” backup because it’s on all the time, a file server so I can share my files across my devices easily, and a media server. The NAS I use is QNAP’s TS-251. Its contents are basically a mirror of my external hard drive. A 64GB thumb drive and assorted DVDs. I keep my digital pictures and documents in these. They’re in my fireproof safe box. Similarly, I have those same digital pictures and documents on my OneDrive account. Because it’s on the internet, and perhaps because Microsoft (and probably many other free cloud storage services) snoops on the files for marketing reasons, I have them in an encrypted 7zip file. As of 7/22/2017, I'm considering another online storage solution since OneDrive came with an Office 365 subscription, which I let lapse since I had no need for it anymore. I used to do a purely manual system of copying and pasting the contents of my computer into the backups, but this soon became cumbersome. One of the biggest issues is sometimes I rearrange the contents to either get rid of stuff I don’t really need or to reorganize them. If I copied and pasted it over to the backup, I’d get a mess in the backup. Otherwise I’d have delete the backup and then copy it over, which is risky (I have one less copy, and if it's the original and it gets hosed, then what?)
I found a program called FreeFileSync which lets me compare directories, then shows what files are in one or the other. I can then either do an update, which will copy the files that are new or updated, or mirror, which will make the destination directory match the source. So here’s how I put this altogether in a backup session: On my data drive, I have a set of directories similar to Windows libraries. This setup is mirrored on my external drive and NAS. Use the update function from my computer to my external drive. If I need to make adjustments on my external drive, I do so. Use the mirror function to copy the contents of my external drive to my NAS. Once in a while, I’ll update the thumb drive and cloud storage. It’s not as often as the above, which I try to do once a month.   Feel free to pitch in your recommendations and plans!