just find the relevant keywords which are in low competition and good search. You can get help from Google Adwords for Keyword generation.
Well i thinks first of all whatever keys you select should be relevant to your industry and then these keys should be mix of high and low level competitive keywords
Yes, first you see same theme of site of you site in google and pick common keyword from this site and check in google adword and select best keyword. you always choose the low competition and high search volume keyword.