Even if you are in a competitive field, you can still get keywords for pennies if you can work your way into a good QS with AdWords. I have a campaign in the field of a certain type of rehab, *highly* competitive, with average CPCs of $25 and up. But, with a combination of targeting lower positioned ads (#5-8) and writing really killer ads combined with what I think is a good and informative landing page, my ads are running along at 12 cents per click, and my QS is listed as great. But that's not something really you can TEACH someone - you learn by doing, and doing and doing and making mistakes and losing money and learning some more until you figure it out.
You have to really know your market. You have to really understand how AdSense (or YPN or whatever) works. And you have to REALLY REALLY know how AdWords (or whatever your PPC program is) works.
Quality Score is the thing that can kill you in AdWords. If you can master your way around that, you have a real good chance at making it work.
The best tutorials on AdWords that I know of are the online training lessons that Google puts up for its Google AdWords Professional (GAP) program. This is the stuff we have to study before we take the test to certify, and it includes lots of information that (stupidly) isn't even in the help docs. There's also a kind of overview of Analytics. You don't have to be a GAP to use them, you don't have to even intend to be a GAP, and it's all free. They have CBT video lessons, and text lessons, with sample quizzes at the end of each one. Go check it out. Go through the whole list, and when you're done, go through it again. And if you really want to get serious about it, the next time an AdWords seminar comes to your town, register for it. It'll be the best $295 you ever spent. I started making more money with AdWords / AdSense the very night I came home from the seminar (and I considered myself an advanced user even before I took the course).
Here's a link to the AdWords Learning Center with all the lessons. Good luck:
http://www.google.com/adwords/learningcenter/index.html