It might be worth your time to go check out a university near you. There are a lot of warm up exercises out there, but the most important aspect of it is that it works (is appropriate and helpful) for where YOU are at with your playing- if you're willing to cough up something around $30 you can probably schedule a lesson with a college teacher who I'm sure can point you in the direction of some warm-ups and exercises that will get you going in the right direction- as well as diagnosing whatever chop/ sound production issues you may be having. As an alternative, you could go to a High School band director for a lesson as well- probably half as expensive as the collegiate route, although the quality of instruction wouldn't be the same- Especially from any non-brass player. I'd love to help you out with some concrete stuff- giving you names of lesson books etc, but that's tricky (and dangerous) since I've never heard you play before. Hope this helps!