I guess I should have said what I do now. First I look at a map of the whole area and see all kinds of Nat'l Forest. Then I ask, what is close to me (say w/in an hour).
Each Nat'l Forest has a pocket map that shows the different Districts and where is the ranger station for it. Then what I want is the District map, that will have (as far as one assumes they are up to date) all the F.S. roads on it and other nice info. Some maps have topo if they don't I have other maps for that. So I can know beforehand, what looks like it might be interesting and where there are huge changes in elevation because you -know- that's going to be steep. Most of the roads go up because they are there for the fire crews to get there. Speaking of which we have a lot of wildfire right now the atmosphere is "unhealthy" my eyes were watering last night.
Some roads follow creeks so there it tends to be water and maybe mud but those aren't so common.
There's also online F.S. vehicle-use maps (pdf).
Once I decide, ok, I'm going to try going to some spot, I like to have a backup plan, because sometimes you get there and the road is gated. But usually there's other options close of places to go even if it's not offroading there are things to do and see for an outing. I don't like to drive somewhere then go, oh, it's blocked, let's go home. Nah.
I try to call the ranger for the district so far not lots of luck with that. I was hoping they might tell me condition of roads, who knows. I suppose part of the doing of it is finding out. Some places like Potts Mt road you just know from various sources, you will need basically a rock crawler to get through there.
I also look at Google maps and Google earth 3D as part of it. But I don't go somewhere and not have paper maps and a compass and so far I never didn't know where I was. I do really like the GPS showing me exactly, which I have, but I can't reset destinations / waypoints because Google maps is online software and I haven't tried the offline maps saving yet so that's the next thing.
Probably I'm not eager to spend $3k on a nav system and looks like way overkill for me. I think I'd get the Xoffroad app, not expensive, and you can get all the property lines so I'd know definitely when I'm on the forest. I realize you still have to download the maps for offline use but I'd think once you've done that, that since the app is resident on the phone/tablet vs on a server somewhere, you'd be able to reset destination.