SEO Moz has a great section for members that allows you to check a specific page on your site and it gives your page a grade based on the keyword phrase you are targeting. Sometimes this isn't practical if you have very little text on your home page, but its still a good rule of thumb because you can still modify your meta, alt image tags, and even a powerful footer line to engage the user. Just don't try to fool Google by adding a ton of keywords at the bottom of the page using the same color as your background. Google isn't stupid and will flag your site immediately.

Keep the home page clean and if possible, use as many keywords as you naturally can, but keep in mind the user. You don't want to scare the user away when they notice you are trying to dupe them with forced keywords.