Your ranking is dependent on the following criteria, in this order:
1) Views
2) Subscribers
3) Favorites
4) Likes
5) Comments
Keep in mind, it's a combination of all of the above, however. You might notice that a video that is top in the rankings for your keyword may have only a couple thousand views (and you have 20K + and are not on the first page). Take a look at their subscriber count, favorites, etc. Are they out-ranking you there? Also, pay close attention to the tags they're using. Yours may not be optimized.
Finally, there is a lag on YT. You may be on your way to the front page but it can sometimes take a week or two to land there (even though you out-rank your competition).
Also, note that while Likes and Comments are nice to have (and add to the legitimacy of your vids), they don't weigh heavily in the rankings.
Hope that helps!