I do it, but not in QLD. It's getting more and more stringent here in NSW, our fav riding places becoming national park and closed up. Only way to get a decent ride in is to ride the many illegally created single trails.
Generally if you're riding them but are fully registered, you'll just get a warning / slap on the wrist.

Just curious. what sorta riding experience have you had?

anyway

first thing I would recommend you do is get your license sorted, if you want to keep it legal, your vehicle has to be registered to ride it in a state forest (permitted areas). if you don't want to go down the path of license and registration, you're limited to private / club property.

If you've got your open car license you can apply for RE-L (moto learners) once you've got that, you can do a 1-day q-ride course ($350ish) if you've had motorcycle experience, or a 2 day if you haven't (not sure how much 2 days costs). And on completion you'll be able to get your RE-O which is your restricted opens, which basically means you can ride unescorted on restricted or LAMS approved motorcycles, which wont be a problem because pretty much every single trail bike you can imagine falls under LAMS.

As for riding spots, there are some places Ipswich way, one near beaudesert, just past the bridge (google it), apparently its legal and free there, even for unregistered bikes, but it is mostly sand from what I hear and that can be a bit tricky if you haven't ridden on it before.

I go to glasshouse alot and that place is awesome for bikes / 4x4s, its about 1.5 hours for me to get there, but I reckon its worth it. You'll need to be registered if you don't want any trouble though, I see police up there all the time getting people for riding non-registered bikes, usually at the entrances. And there is also Mt. Mee, out past Dayboro, you'll need a license there too.

Places closer to the GC I'm not really sure of to many, but would love to find out more as its closer to me, mount tambo has some tracks, I'm not sure exactly where they are but there is a club that does monthly trail rides, rtbc.net.

trail riding is fun as fuck

Couple of my mates do it.

Closest place I can think of to the GC that's 100% legal is the new(ish) Moto park at Wyaralong dam. Don't know if any of them have gone there yet.

Others, Various cost, more of a Weekend trip:
Emu Creek
Rover Park
Black Duck (Needs yearly membership)
Manar Park

Free, fairly close, areas that I'm pretty sure are legal. They are for 4wd's at least. Probably need a registered bike (?) and your license;
Glass House Mountains
Back of Mt Mee / Dayboro State Forest

Free, Fairly close, areas that I'm pretty sure are not 100% Legal;
Ormeau
Pine forest behind where they're building Yarrabilba (Though... a lot of it is Yarrabilba now... stupid development)
Pac Pines