Read this: http://damonrinard.com/aero/aerodynamics.htm

For those who loathe reading lots of words, there is a table 1/2 way down the page. While there is a lot of other material on the Web this one page does a lot to explain what you need to know with regard to the basics.

Note to Fore: Shaved legs are on the list. 5 seconds saved on a 40k time trial.