The best thing you can do is set up Conversion Tracking. This allows you to know if your advertising is getting you results. You can track conversions down to individual keywords and move your budget around for keywords that are more successful for you and also nuke keywords that aren’t getting you results.
Setting up your conversions can be simple. If you are using Google Analytics then you can track the number of times people land on your “Thank you” after filling out a contact form.
If you aren’t using Google Analytics, then you just put a small piece of code provided by the pay per click services provide on your “Thank you” page.