Welcome to the competition GrizzlyGames. Good tutorials are in the help files. I'd say that first you need to understand the tools then practice using them until you're good
I've been recording some videos from those speed modeling comps. Check them out here:
http://www.andrei313.com/makingof/
We have a good
tutorials section... and as far as other sites go I'd say that
www.3dtotal.com has a very nice collection of tutorials for beginners. You can also check out
www.evermotion.org