The forum library [webmasterworld.com] is a good starting point.
In your work to improve CTR, ad copy is important, but the keywords and matching types (including negative keywords) will make a much larger difference in your CTR (and therefore your costs and your position). Don't let you ego encourage you chase every possible (peripheral) click that may occur, go for the most targeted ones and your ROI goes way up, CTR goes way up, positions go up and costs go down.