Fuel tank!

My truck won't be running for another year so how should I keep my fuel thank clean on the inside until I start using it again?

Open the fuel filler cap, then open the drain plug underneath the tank so the fuel can drain into a gasoline safe container. Let the tank evaporate for a few days with the filler cap open and drain plug out (obviously do this is a well vented place where there's no open flame). Replace the drain plug and maybe add a splash of Sta-Bil to neutralize any leftover puddles of fuel.

Then drain the sta-bil? And the tank can just sit until I'm ready to use it?

Yes - you could also run the truck until it quits after you drain the tank to clear the lines, or add stabil to the fuel, run it a minute, then drain the tank.

My truck is comepletly apart it won't be running for another year!

Then drain the tank and take it to a radiator shop and have it boiled out - then it will be clean as can be and you could even use a tank coating kit on it while you are at it.