Establishing a regular measurement program will enable one to judge the true effectiveness of paid search campaigns, which are not always as clear cut as a measure of pure profit...
Use unique landing pages
Unique landing pages will make conversion tracking much easier as well as allowing for greater segmentation of campaign keywords, thus gaining a top quality score (and minimizing the cost per click as a result).
Understand the objectives
Before spending anything, there needs to be clearly spelled out goals - whether they are to drive traffic, gain new eyes on site, get a white paper download for though leadership, drive newsletter signups for drip marketing or gain direct sales on that visit.
Consistent measures, consistent reporting
Even simple spreadsheets can make the data presentation orderly, given a consistent dataset and make it easy to spot trends, dips, wins and identify issues of concern.