Back when I started forums I had a tried and tested method - it sounds odd but it worked for over a dozen new sites I've opened during the last 10 years. No matter the software. vB, XF, IPS, custom software, whatever.I usually invited a few friends from other forums. It's important to not spam the forums. I can't stress this enough. Do it in a way which doesn't cause a mass exodus and doesn't anger the community admin. It's often a good idea to include the community admin or get their permission beforehand. Luckily I had a forum which I was a staff member on and eventually bought which I was quite close to the admin and he was fine with it, as long as we all remained active on the origin site and it didn't directly compete. In my case I started a graphics community with members from a general discussion community which didn't have a graphical element, so no competition and nothing which catered to that crowd. We all posted on both sites and it worked well.I then introduced post exchanges with other sites. Affiliations with those same sites so we became sort of 'friend sites' or partners so our memberbase was very shared, but we all catered for very different needs. You're running a psychology forum so perhaps find like minded people on general forums. Again, do it in an above board manner, no spamming and no direct advertisements unless it's allowed. There's also services like Postloop (my referral link if you are interested, or just postloop.com) which popped up after I started forums which are great for supplemental members and posts from outside of your core member group. They're very temporary, but it's also a great resource for the aforementioned - find forums, affiliate, make friends and network. It's a lot of networking in the beginning. You'll spend as much time on other peoples forums as on your own.I also used things like Twitter. I have been lucky enough to have a relatively large Twitter following who are forummers because of my history with forums and software, freelancing, coding for various platforms, building my own, etc. It helped drive clicks to my site and registrations.No matter how much traffic your site gains, make sure that it's INTERESTING. You now have the eyeballs, but you need to keep them on your site and convert them to members. For this you need incentivisation, interesting subject matters, and dare I say it - @Rikki's "mot du jure" - gamification. I believe this is why XF started out so strong, the Trophies system. It's easy to do this without systems though, you can have Member of the Month contests, posting games and all sorts of other things. Of course, IP.Board 3.x has the Awards system and countless other mods which make this happen. IPS4 no doubt will have even more gamification options as Rikki and Charles are very fond of it, if memory serves and I think it's even on the feature list for future versions.