How Can I Improve the SEO on a Forum-Oriented Website?
This is a bit harder task, but not impossible.
As you go through all popular forums, you can see that they have a various kinds of niche related Categories and Topics! This is the first most important thing what your forum needs to have.
Secondly of course you need visitors.
Allow people in your online community share their answers by adding a share widget, where you will be also sharing their/your answers on social media as often as possible to bring attention and visitors on your forum.
Thirdly register and be active on other forums which are similar.
Try to motivate your visitors to be more active by asking them a questions on your forum, pretending to be someone else. Its nothing bad, it will just makes them to come back!
Also answer all questions asked on your forum to keep visitors coming back and ask more and more! Be an EXPERT, HELP THEM!
Let them to use a signature links on your forum FOR FREE!. Yes I know maybe you need to monetize this forum asap, but at the beginning you need to offer almost everything for free to build a good name and have more and more visitors.
Create a small marketplace on your forum as DigitalPoint, BlackHatWorld or WarriorForum do it will makes them more happy by promoting their products or services for free and be sure, they will share their Sales Page (on your forum) to others and this will brings you even more targeted traffic!
That would be my recommendation for you which Im sure works if you will be working on it and wont charge for everything at the very beginning!