Search for each keyword related to your field in Google and examine the top ten results.
You must spend 10 to 15 minutes on EVERY keyword that you run through Google.
Remove keywords where there are many sites with superior authority on the first page.
The good things to find are:
If you find a lot of these types of results, you can probably overcome them.
Make sure that the keyword you choose has enough searches per month to justify the work. Also, make sure that the intention of the searches allows you to convert them into a profit.