As I've learned around this forum,
SEO is very important. This stands for
Search Engine Optimization.
In a nutshell, this means titling and tagging your videos accordingly so that YouTube's engine pulls them into the search results more often, thus getting you more views and interaction on your videos. And yes, tagging helps tremendously.
So for titling, if you have a video of a guy riding a bike and wiping out,
don't title it "How did this happen?!" as if it were a vlog. Those kinds of titles are okay for current subscribers and grabbing their attention, but not for getting new views.
Instead, title it
"Guy Wipes Out and Fails on Bicycle" because that will engage the YouTube engine more!
Secondly, always interact with your viewers! Tell them in your videos that if they enjoy the content to subscribe and comment below! AND ALWAYS REPLY TO COMMENTS!
Third, find ways to promote on Twitter using hashtags to help you out, and post highlights of a video on Facebook that you feel your friends would share around!
Lastly, patience. I've had a few videos grow steadily since they've uploaded, and some have fizzled out. It's the luck of the game of YouTube. Just be patient and don't give up.