Be sure to rest as much as you play. Don't beat up your chops. If you can find it, Leon Merion's Trumpet Isometrics (try Brasswind and Woodwind) has a great text section which may answer many of your questions as well as a bunch of good exercises. I like the Walter Smith Flexibilities. I think they are easier to get into than the Colin Advanced Flexibilities. I would second the recommendation for the Clark's Technical Studies, practiced exactly according to the text.