If your doing the whole truck I'd suggest removing the bed and front fenders so you can do it in sections. That would make it a lot easier. Wash everything very well with soap (I prefer dawn). WET sand everything with 200 grit sand paper (or sponges, better yet DA sander). Wash and rinse once you do that. Then repeat using 350 Grit and then 600+. You will hate sanding by the time your done. Others may chime in on what grits to use, its just what I'd do. If you feel you need a higher grit sanding to make it smoother don't just brush that notion aside, Do it. It'll save you from redoing everything again. After your done sanding wash with a heavy duty cleaner such as TSP. TSP leaves a residue if you don't rinse VERY well. I used it doing my interior and much of the exterior and I've had great results. Then of course mask off what needs to be protected and shoot light coats of etching primer and several light coats of your paint/clear coat. It'll take time but can be done to looking professional even with a rattle can if you have the patience.
Most of the time the truck being your only mode of transport works against you.