Keep your video short and funny. The title and content are very important.
Share your video on your Facebook, google plus, Blogs etc to increase the viewers and give them a reason to subscribe to you.
You could plan some Giveaways, Contests, and Sweepstakes to attract new followers and increase the subs
There are also may paid ways to increase your subs, you could collaborate with other media, channels or forums, etc,etc