I've found Wordtracker to be the easiest to get started with. You can enter in keyword phrases on their home page and get instant, actionable advice. Then, after you've made a few choices in Wordtracker, go to AdWords to compare and refine your results.
However, here is a down-and-dirty way to find out high-traffic keywords:
- Go to Google.com and log out of your Google account.
- Start typing in your search terms
- Google automatically returns the most-searched terms while you're typing.
