PPC in extremely competitive.
Think about it.......
instant traffic for any keyword you care to bid on!
Traffic generation just doesn't get any easier than that, and everyone and their mother is competing for a a piece of that action.
mikebrad is correct. Quality score is key.
You need to get your cost per click down and bump your competition to earn decent ROI.
The free PPC book by Aaron Wall, and recommended by Jeremy, is a good start but you'll need a lot more advanced strategies to beat the PPC game in any profitable niche.
Perry Marshall's "The Definitive Guide To Google Adwords" is considered the bible of PPC....well worth the 49 bucks and I recommend it.
http://www.perrymarshall.com/
There is a huge amount of PPC info on YouTube and several forums dedicated to PPC..... just search and you will find.
If you have any specific questions about PPC you can PM me.
Dave