It's okay to be negative (when it comes to keywords). Negative keywords are a tool for excluding search terms that may be irrelevant to your product or service from your campaigns. Negative keywords reduce wasteful clicks, which result in inefficient spend as they ultimately have no possibility of converting, and will help to achieve efficiency quicker since you'll be able to gather clicks on more relevant keywords. For example, if a hair care product is designed specifically for women, the negative keyword "mens" would be effective in reducing unwanted traffic. Negative keywords are applied at the campaign level by match type which allows you to achieve more (exact) or less (broad) specificity, depending on your needs. Err on the side of greater specificity, as introducing negative keywords may reduce the search volume that you are trying to get in the first place. Got it? Good.
Sweep it up. Negative keyword sweeps should be completed daily for the first week or two after launching a campaign, and sometimes a couple of times a day if you are managing a higher spending account, to ensure you quickly negate all irrelevant traffic. After campaigns have been running for some time, its a best practice to complete sweeps every week to eliminate irrelevant and inefficient traffic.