Check out the google help. Use google keyword tool for keyword selection. Know about "exact,phrase and broad match keywords". They play a very important role in improving your CTR(click through rate) You need to split test your landing pages for improving your quality score(You will find good amount of information on quality score in google help.) As a starter, try staying away from money making niches. They are a big no no!! You are sure to run into losses... Apart from this, I have exclusive case studies on PPC landing page makeover ,PPC traffic by Anik Singhal. These case studies are only available to members of Affiliate Classroom. I have personally spoken to Anik to get these case studies. PM me, if you want access to it. Another very helpful guide is - free PPC report by Amit Mehta, the link to which is given in my sig. Trust me, its worth reading. You'll really get to learn a lot about PPC..
Keywords are important ! Niche is important ! Your site ( if you have one ) is important ! Watch out for too expensive keywords ! Be sure you get profit ! www.hubpages.com/hub/Adwords-Manifesto-Review
My top tip would be to join twitter and find lots of AdWords experts to follow, as you will receive lots of hints, tips, and links to the latest AdWords information. Follow me at http://twitter.com/clairejarrett