You can of course plan the big lines of the campaign, but the more precise you get and far ahead of the present, the more you will either lose or railroad to not lose. Both suck
Same. I've come to realize the more i plan, the less flexible i am and it leads to bad improv.
At this point i just think of a couple story beats or cool scenes i want to do, then we start rolling dice and see what happens.
I think the player types is important.
I've had players who will engage with stuff and make good things happen, and then I don't need to play very much. They'll see the awkward tavernkeeper and the village blacksmith and run cheering into ROM COM TIME. Can't really plan for that.
But I've also had players who are just wallflowers. They don't take initiative. They don't push for their own goals. They're timid and easily discouraged. "The tavern keeper doesn't want to give you the staff. It was his grandfather's, he says, and he doesn't want to hand it out to just anyway." "Uhh.. uh.. ok.. i don't know what to do. Can I charm person him?" "You can, but that's an escalation and people will be mad if they find out." "Oh nevermind I don't know what to do."
Meanwhile the other party got the staff by getting him and the blacksmith to finally go out on a date, and now they're all on great terms.
The timid party needs more planning (but still only a session or two in advance) because otherwise they're going to just stall out and get frustrated.
Maybe one day I'll have a group that's consistently engaged, thinks about the game between sessions, and knows the rules of the game reasonably well.
I always over plan things. I'll plan encounters appropriate to level. I'll plan NPCs. I'll plan dungeon themes. But I won't plan a dungeon themed encounter unless I know they're heading into that dungeon because it's where we ended the last session.
To put it another way: I never plan so specifically that a thing can't be moved to another place unless I'm positive it's coming next.
I mean, you should have the current adventure planned. That's probably ten sessions, right? If it's a bigger dungeon it might be 20 sessions.
Do you send your players into a dungeon without designing the dungeon first? What the fuck.
You should also always have at least the beginning of the next adventure planned, because at any time, the players might decide to give up on this one and move on to the next one. This could happen because they run out of clues, or because they think it's less important than their other goals, or because they disagree with the NPCs trying to get them to do it or for some other reason. They could also try to do the next adventure and this one simultaneously, especially in an urban campaign where everything is happening pretty much in the same place.
Stuff you planned that the players don't do is WAY better than stuff you didn't plan that the players do.
