I have definitely come across the same problem,
AnEmerald.
Firstly, what kind of threads do you enjoy making? I'll list a few below that might peak your interest.
Whenever you think of an idea, write it down. It comes in handy later on.
What about -
A useful guide - Maybe there's a gamemode you're good at and have a few nifty things you can teach others. OR, everyone always loves a well-done Guide To A Good Staff Application!
Tips&Tricks - Much like the before suggestion, some tips&tricks for applicatants? Tips&Tricks for something else in game? Play around with it.
Your thoughts on something - You could make a thread about your thoughts and opinions on something server related, or even non-server related in the "Off Topic" section. Or asking other people about their thoughts on something?
Start one of those game things - People are always coming up with cool and fun forum games, like "See how high we can count before staff post", or "If you could have any username, what would it be?". Stuff like that get people engaged and bring the community together.
I hope this helped in some way, I wrote down all I could think of. Look at some different server forums for insperation, but remember, don't plagerise. Best of luck!