will try to help you out.
First, use the AdWords Keyword Planner tool and check to make sure that the keywords you have selected actually have significant search volume. Check the Keyword Status column for low volume, Below first-page bid estimate, disapproved keywords, or site suspended messages.
Learn how to check and understand Quality Scores.
This video will help you understand how the ad auction works and the importance of ad relevance and Quality Scores: