Here’s a PPC keyword strategy you might want to consider:
Phase I
Use highly relevant keyword phrases of at least 2 words. Try to find as many as possible. The limitation here is that you will not be able to find them or get enough clicks on the ones you do find. In some industries these keywords will be sufficient to make your campaign successful and you will go no further. This is where most people have a problem, they are cannot find enough keywords and people are not finding your site. This is the biggest wall to overcome.