www.bbtrumpet.com
very good site about trumpet playing concerns. Playing PP and softer was about the best thing anyone could have recommended to me. It helps develop control of your aperture. Basically, any ape can pick up a horn a toot loud notes, but learning how to play soft is where I think it's all at. Training a smaller aperture also helps with higher notes. I think it would be impossible to play a double G with the aperture size of a low G below the staff. But like daniel said, balance your practice volumes. Warming up at PP is very effective as well, but more importantly, develope a consistent warm up... or find something that you do everyday before you play. This will help develope you as a consistent player which is very important for any brass player. All brass players have there "good" and "bad" days, but by being consistent, you won't have to worry about whether it's a "good" or "bad" day to play a piece. As far as opening up and playing loud and higher, I think it's better to do that towards the end of a practice session. First, you don't want to kill yourself before you get into more refined studies such as maybe arban or clarke. By playing loud and high at the end of your practice session, you should be able to develop endurance to knock out any fanfare. As far as method books go, I recommend
Arban
clarkes technical studies
clarkes 24 etudes and solos
max schlossberg daily drills and technical studies
james stamp lips drills
colins lip flexibilities
36 Transcendental Etudes for Trumpet