SMF can be a difficult one to
SEO for. There is this one kinda big SMF forum that I am a member of. It has 52,127 threads, and 629,718 Posts - google has only indexed 1,820 pages of that forum.
From around July 2008 - January 2009 I ran an SMF forum. When I switched to
VB in Janaury, the number of pages that google crawled daily went up by 4 or 5 times.
I highly recommend a sitemap generator, and put some site links to some of the important sections in the footer of the forum.
If you have a blog somewhere, provide site links to some of the forum sections, and deep link to some of the threads.