One thing I haven't seen mentioned is that different tubulars fit differently, so some combinations are easier to work with than others.
With fat tubulars, such as Campionato del Mondo and Paris-Roubaix, I've found that a bit of air in the tubie helps keep the sidewall from picking-up glue from the rim as it's installed.
Barum flat-molded tubies were best left empty during installation.
Some Gommitalia tubies will flip sideways (one sidewall toward the hub, one sidewall to the outside) with the least bit of air inside. They will even roll over when stretching on clean rims, and will try to take this shape again when glued on. Thus, it's best to inflate them very little when they are first installed, and only bring them up to pressure after they've set for a day.
If you don't mount tubies very often, it's a good idea to practice mounting your new tubie sans glue on a clean rim, to discover any complications before there's glue involved.
Aldo Ross
Monroe, Ohio