About the 5th one you figure it all out. Up until then, you have a learning curve. I'd suggest clicking on my tutorial, it will it get you a pretty good idea. But be prepared to spend about 10 hours on the whole job...or 1.5 days... if you want to do it right.It's much easier after you've done one but the first one is a biatch.
Actually, I found removing old tolex that had probably been applied with hide glue came off rather easy. If it was newer and used a spray adhesive, that might have stickier, but I suppose some solvent or goo-gone would help.My bet is removing the old stuff is the hardest. I've done my own stuff quite a few times when it was new cabs I built, but never reworked an old one.
Dunno what the pros use, but contact cement is what I used. You need to do this outdoors or in an open space...not in a house...too much vapors & cover the floor with some plastic.