I've never been any good at creating my own adventures, but give me a module and I can run the heck out of it. I think that adventure modules or scenario books add an heir of familiarity to the game system. Modules can also be good tutorials on how the rules of a particular game works and how a gamemaster and can use the rules in certain situations.
Decipher please help us plot-challenged players and put out some adventures.
Da Guru
Space: The Foodless Frontier...
Star Trek for the D20 System
http://groups.yahoo.com/group/startrekforthed20system/