1. Create a keywords list not only fit to your product or service, but also your business and your competitors.
2. Create a list for those misspelling or typos keywords.
3. Rank #1 brings most clicks but it is expensive. Rank #2-#4 can give you more visitors with less money.
4. Put your keywords into the headline. This can attract more clicks.
5. Give a reason in your ad why visitor should click on it.
6. Prepare a list of “exclude” keywords. These will stop the advertisement to appear in non-applicable search.
7. If you want to avoid those “free-stuff searcher”, mention the price in your advertisement.
Okay. It is a good guideline for starter.