Three things to know about Negative Keywords:
1) Try starting your campaign off with broad and phrase match keywords. Let the campaign run for 2-4 weeks and then use Google's Search Query Report to identify terms that are actually being typed into the search bar.
2) Review the report to identify possible negative keywords and potential new exact match keywords that are receiving strong conversion rates. Use negative keywords to prevent your campaign from wasting clicks on terms that are not converting. Examples may include words like "free" or "cheap," or terms that may be homonyms with negative connotations. I.e. a Coca Cola campaign may have the word "coke" in it's campaign's keyword list, but many negative keywords would potentially be needed to filter out those searching for cocaine related topics.
3) Google allows up to 10,000 negative keywords per campaign. Feel free to be liberal with your application of negative keywords. Google's free "Adwords Editor" allows for easy uploading of multiple negative keywords across many campaigns/groups. Run a new Search Query Report at least once a month and identify new words to add.
