You could use the keyword suggestion tool here,
http://www.digitalpoint.com/tools/suggestion/
Find the keywords with the least competition but with at least 50 searches daily, use them.
To see which has the least competition, search the keywords in msn.com, yahoo.com, and google.com and check the results.
For example, I did this with "birds", in Google I get, "Results 1 - 10 of about 182,000,000 for birds" that's a lot of competition so I go back to the keyword suggestion tool and try out the next keywords in line, and so on, until I find one with at least 50 searches and the least competition.
Then it's worth investing your time in.