Back in 2001 the US National Transportation Safety Board published a report on the survival rates in air crashes (PDF, 800 KB). They are much better than you might think:
Nearly 96 percent of the occupants involved in a Part 121 aviation accident over the past 18 years survived the accident, and in over 46 percent of the most serious of these accidents (accidents involving fire, serious injury, and either substantial aircraft damage or complete destruction), more than 80 percent of the occupants survived.
Nonetheless, there are several things you can do to improve your chances of surviving a crash. There is an article on Wired’s “How To” Wiki, summarising the main points – it’s not long, and is worth reading if you are going to be flying in the near future.