Do some homework on URL rewriting.

You maximize your exposure to th engines by re writing on target keywords.

Don't be too broad, narrow down to only relevant subject matter and tag urls with keywords.

Can you give some details about URL rewriting?

through link building and social bookmarking!

Your mean linkexchange?

link exchange is part of link building, others techniques includes:
* forum posting in related forums
* ads posting
* RSS Submission
* Directory submissions
* Blogging
* Viral Marketing with ebooks on forum marketing
* Comment Posting on related sites
* social bookmarking
* press release make it news worthy

I forgot to optimise your Forum for SE
* Avoid duplicate content - Multiple links to the same content can ruin your site in the search engine rankings.
* You should get active meta tags
* Get links to your content
* Avoid forum bloat by really thinking if what you want to do adds value to the site for the search engines and the visitors.

Hope this will help, i will join your forum soon cos an a Nigerian.

Thanks Hafsoh and others.

also the naming convention of the categories of the threads will help... just make sure they default as the title

They do already.