DMNews offers some helpful suggestions on maintaining your pay per click campaign (PPC) on a strict budget.
1.  Distribute your efforts- Utilize all search engines for advertising, not just Google
2.  Use Negative keywords
4.  Choose when your ads are “live” wisely
5.  Geo target
6.  Analyze your reports regularly

When starting out not everyone has all the knowledge and money to do advertising effectively.  Therefore, researching and trying to listen to other expert’s advice is probably the best way to roll out a new PPC campaign.  Many publishers I deal with at Leadpile Lead Exchange have an ability to have a large ROI, but not if they are not running their PPC campaign effectively.  No matter what network you are doing lead generation in, utilize the search engines reporting AND your affiliate manager to help you fine turn the pay per click campaign.  REMEMBER:  A successfull PPC is also beneficial to the network you are doing lead generation with.  Therfore, it is in the best interest of both sides to make the PPC campaign work effectively.