Adding negative keywords to your account is one of the best methods you have at your disposal to improve your Quality Scores and weed out irrelevant clicks. A good list of negative keywords will ensure you are not paying for traffic that you already know will not convert to sales and leads.
You'll need to do some research to generate a thorough list of negative keywords. Part of this process is using your common sense and thinking of potential related queries that will not be relevant. Aside from brainstorming potential negatives, you can also use the following tools:
Google's keyword tool: Type in the most general keywords you'll be running in your campaigns to see other related terms that people are typing in. Anything that does not apply to you is a good potential negative keyword.
Google.com: Search your most general keywords and pay attention to both ads and search results. Are some of the ads and search results that come up related to products...