For Pay-Per-Click campaigns, such as Google adwords, don't just rely on using top keywords for your ads - this is the cause of many failures. Paying towards top keywords will yield you poor results as competition for these is already high. You should go for long tail keywords that are more likely to yield specific results because specific searches on long tail keywords or phrases are the ones that usually convert.
Remember that Pay Per Click is trial and error, especially if you are new. Be careful how much you bid at first, and find out what keywords convert in your niche after a test run so you know what works and what doesn't.
Also, don’t just use Google adwords, try out several pay per click services and see which one works best for you.