I owned a mybb Forum for a while, umm I would like to make a few suggestions.
The template is kinda plain for me, i suggest finding one here http://www.awesomestyles.com/mybb-themes
They have some nice styles there and there pretty easy to install.
Create a logo and design so custom graphics to make your forum stand out more, and after that the design may look pretty clean.
Just tryin to help out
Maybe increase your Categories to a minimum of ten different subjects, using sub-forums for each one.
You’re limited (free account) to how you can stop spammers, without the use of good scripts to minimize their effect, so make sure you backup your forum as the first thing when you enter the forum each day, not last thing before logging off as you soon learn the habit of not backing up to your cost.
Your style/design is simple/neat, it’s the subjects/threads you might need to spice up.
I’m not sure how much control you have on adding things/gimmicks to your forum so look around other (free account) forums for ideas to use on your forum, signup in the ones you thing might help yours and ask for tips.