Depends on the keywords, generally for any clickbank products or store products I will locate the high traffic keywords which have low advertising competition.
I'll then put them into a google adwords alternative like AMP Keyword or Questclick, and let the sales fly. At this point I don't use Google Adwords anyway but when I have I would set it at $0.28 per click, for the keywords that have the lowest advertising competition. That's how to do the right thing with adwords.