Tip #9: Be a bad speller... or at least know how to be one.
You would be amazed how many times people misspell or mistype common words.  For example, if you sell refrigerators, use "refridgerators" as a keyword possibility as well.  People are in a hurry, and you could use their mistake to your advantage!  I used to blog on other websites, and sometimes my posts with a spelling mistake in them brought me the highest number of hits for that reason alone.