Once the tracks are adjusted properly, meaning the tank drives straight and they generally stay on under different conditions, they won't need readjusting unless you change the weight of the tank, alter the suspension or if the suspension weakens over time. Each tank brand and model will have a different adjustment system, so you'll need to be specific.

An important tip is to store your tanks on blocks high enough to keep the roadwheels off the ground. I buy an eight foot section of primed square molding from Home Depot and cut it to one foot lengths, screwing/glueing two together. That way it's just barely off the ground and less likely to tip over. Some guys use 4X4s, bricks etc. I stored my Tamiya Tiger for the first 8 years or so on it's tracks and it fatigued the torsion bars and settled down to zero suspension over time. It's also important since it keeps the tracks off the ground in case you're doing some work with it on and don't want it to jump off the table in case you bump the throttle.

Removing the tracks is something you may have to do occasionally, or at least remount if they pop off. I took a small screwdriver and embedded a track pin in the handle. which works well to push a track pin out enough to get a pair of pliers on it. When you put the tracks back on, it's usually easiest to couple the sections together on the drive sprocket, it holds them in space at the proper distance.

I keep the gearboxes lubed with ceramic grease. It's what Tamiya uses and it's plastic safe. Don't buy Tamiya's, you can get much larger quantities cheaper from other sources. Fishing reels and bikes use too, so they're a good source. I'll clean the gearboxes if they get really dirty, but otherwise there's not much to do. Some guys will completely clean and degrease regularly, it's up to you and your preference. My Tiger I gears are running fine after 10 years without trouble and they haven't been cleaned.
It really depends upon use and conditions you run it in.