Here's a great reference on how to write effective adwords ads. It also lists other references so use it as your first stop in your research on how to hone your adwords copywriting skills.
Source:
http://www.site-reference.com/articl...ect-adwords-ad
One more thing, there are adwords scrapers available online so you can see what kind of ads your competition is running. I don't suggest running out and straight up copying them but use these tools to find out where they fall short and improve on their shortcomings nad gain a competitive edge. Key source:
http://www.spyfu.com