Here are a few software-related things to check at the outset:
1) SessionIDs are bad for spidering and indexing - eliminate them for spiders (or for everyone).
2) Static URLs (or URLs that look static) are best, followed by short (say, 1 parameter) query strings.
3) Check the page title and description for topics and threads - you may have to modify the code for these to get clean, relevant titles/descriptions.
4) Eliminate junk where possible - stuff that clutters the page (and code) without benefit for visitors or SEs.