04 Dec 06 4:21 pm
The rule of thumb is, you are looking for the widest ratio between the number of times searched and the number of competitors. The actual numbers will be relative to the size of your niche.
Another thing you have to consider is, you have to think like your customer. What words would they be using to search for my product. You can sometimes uncover words that your competitors haven't discovered yet.
Your goal is deliver traffic to your site and finding the right keywords that will generate traffic for you is most important, so use the numbers, use your creativity and use your instincts that should help you put together a good list.
Hope that helps,