Here's a great resource I found on the Avid Community bulletin boards:
90+ Tutorials on Basic MC tips
One of the board's moderators has been producing short video tutorials on a number of Media Composer-related topics, and has now aggregated them all in one handy list. If you're struggling with Avid or just need a refresher, be sure to check them out.
(Just a word of warning, some of the tutorials are specifically about transitioning from Avid Liquid to Media Composer. If you've never used Liquid, these might be a tad confusing and are probably best skipped.)