Try to avoid the use of image maps unless you include HTML links as some search engines do not follow image map links and therefore they do not help with your search engine optimization efforts.
Use the longer or plural version of a keyword where possible. This is a concept called “word stemming” used by some search engines to return search results that include keywords that extend beyond what the user has searched for.
What this means is a search with the keyword “engine” might return results for “engines”, “engineers” and “engineering”. If someone searches for a longer version of a word and your page only uses the short version, then your page will be excluded from the list of possible results.
You should also sprinkle a few uncommon keywords and synonyms in your main body text. Less popular keywords have less competition when it comes to search engines, so your web page has a greater chance of being listed amongst the top results!
Do not repeat your keywords and keyword phrases over and over again on a web page, this would be considered as spam by search engines and does not make enjoyable reading for your end user!
Search engines give prominence to keywords nearer to the beginning of the text.
Do not use font size one (1) text as the default text size. Many search engines consider tiny text to be spam. It's OK to use some font size one text.
Do not participate in link farms or link exchange programs. Search engines consider link farms and link exchange programs as spam, as they have only one purpose - to artificially inflate a site's link popularity, by exchanging links with other participants.
Do not confuse link farms and link exchange programs with reciprocal linking. Reciprocal linking is the exchange of links with individual sites, and is certainly an accepted technique for improving your site's link popularity.