I'm not sure that this fits in the topic of 'optimising' but I employ a number of techniques to help with search engine rankings.
Some of these techniques are well known, others I have found from my own experimentations.
Mapping
It will ALWAYS help if search engines can actually find the content on your site that you want to promote.
I employ both xml and html sitemaps. My xml sitemap is aimed specifically at google with a specific requirement that it lists my news, content and forum posts.
As forums can generate tons of useful keywords and frequently changing data, to my mind, it is essential that this area is not over-looked.
To help, I utilise one single file called rdf-nuke.php
This file is extremely useful for me as by varying the parameters on which the file is called I can generate an xml output for any forums(s).
For example;
http://www.guildofsecurity.co.uk/rdf-nuke.php?count=50
will retreive a list of the last 50 forum posts.
http://www.guildofsecurity.co.uk/rdf-nuke.php?fid=9
this will return all forum posts from the forum with the Forum_ID '9'
http://www.guildofsecurity.co.uk/rdf-nuke.php?fid=5&count=3
will retrieve the last 3 posts from the forum with the id '3'
I can make any specific url I want and add it to my google sitemap.
I also use a module called INPUT_FIND - this basically allows me to generate forum posts from xml data feeds from other site. This give me constantly changing dynamic content which is both relevant to my site and gives google and others something to chew on every day.
HTML sitemaps should also not be over looked, if nothing else, they can help with keyword count by making use of alt and description tags as well as plain text in the link.
Images
A lot of people forget about image 'alt' tags - take a look at your theme and see how many are actually used - not many I bet!!
Again, this can help toward that elusive keyword intensity count.
Keywords
Keywords and key phrases are king!
There is absolutely no point in going over-board with meta tags!
If you have regularly updated dynamic content - that is your key to success! If you find you are falling short of your target there are some tricks you can employ to give yourself a little boost.
Usernames - they can and will be crawled so set up a couple of dummy accounts using your top keywords and make news and forum posts with these usernames.
Create 'content', 'faq' and other pages that are keyword rich.
If you can do so without misleading anyone, edit forum posts subjects to incorporate keywords and choose your forum category names wisely!
Other
If your hosting account allows you to use sub-domains, don't waste them. Create sub-domains with an 'intro' page with links to parts of your main site. You can create sitempas for these pages and get the search bots to crawl them too.