Look up the keywords used by your competitors in trade journals, Yellow Pages, directories, outdoor advertising posters, etc. Right click and view source on web pages to see what other people are using in their META tags. Ask friends, colleagues and children what words they would type into a search box to find you. Use different META Tags on different pages.
Many search engines use string queries when indexing sites.
Vary the amount of characters on different pages. Repeat your title, main keywords, phrases and abbreviations up to 5 times only. Use commas to separate key phrases on some pages and just use spaces on others. Do not use line breaks. Ask friends and colleagues how they would misspell your keywords.