Think of what words users would use in search engines when they are looking for a site like yours. These are the words you should optimize your website for.

Tip: Ask your friends what they would use for a search.

• Don’t use only general keywords (e.g. “insurance”), but also long tail keywords (e.g. “car insurance washington”). It’s easier to reach a top position with long tail keywords.
• Consider various spellings (time-machine vs. timemachine vs. time machine).
• Keywords aren’t case sensitive.
• Check your Website logs to see if there already are some keywords that bring visitors to your website.

Create a temporary list containing more keywords than you want to actually use. After the keyword analysis you can then pick the keywords that have a greater potential.

SEO Lexicon: Keywords

SEO Lexicon: Long tail keywords

Bing: "The key to picking the right keywords"