Depends what your site keywords are. You need to include meta tags in your header section, alt text on images, emphasise the keywords you want in your actual content. Don't go overboard though. Download Webceo. It's a free tool that will help you to clean up your html code so that it is optimised for the keywords you want.
I recommend you taking a good look and read around this and many other areas of the forum first. You are bound to find many ways to help boost your rankings rather than people going over things that have already been mentioned before.