Beachmystic, my situation is close to yours (as is my age), with some differences. I started learning trumpet and music theory when I was 26, while I had never had any kind of musical education or practice before. I played very regularly for 2 and a half years before life threw a bunch of distractions and obstacles in my way. I was on/off but mostly away from the horn until last August, when I decided to start again.
In retrospect, I know that I was doing many things wrong when I first started, so here is my take on learning as an adult, hope it can be useful to you.
- Get a teacher. I had one, and, as modest as my playing is, I wouldn't have done nearly as good without. Now that I am approaching the edge of where I was before the long break, I am going to get one again, I should have got one from the get go. If affordable, it would be best to have 5 teachers, so that the good advice hammering and bad habits chasing could be multiplied by 5...
- It will be a very humbling experience, no part of it will be ego-flattering for a long time, be prepared for that. Keep your expectations and goals realistic. Set new goals as you progress. You'll read people here talking about 5th grader, 9th grader type of playing. We have to go through these stages but we don't look anything like 5th graders or 9th graders
- Learning the trumpet exposes you to bipolar disorder: some days air slides effortlessly through your aperture, sounds fill the room and you already imagine yourself jamming and having a ball with the big guys. Next day you can hardly produce a sound and it feels that this can not be within the realm of human possibilities. Get used to it, consistency takes time and work.
- Work your butt off at learning to read music. It is as hard, or harder for us adults as it is for kids, our only advantage is better self discipline. Yet, you can obtain suprisingly good results with regular practice. Being able to read opens too many possibilities to try doing without it. No teacher will take you seriously if you don't show an interest in achieving some level of fluency with theory, including reading.
- Familiarize yourself with basic theory, then theory pertinent to the type (s) of music you want to play. Try transcriptions. Transpose simple phrases in many keys. Rewrite some of your guitar stuff for trumpet in a way that will be possible to play. You hear a catchy riff, try finding it on your horn. Be curious. There are many, many musics out there that are rich and interesting, it's all good to know about.
- Listen to your teacher and make every effort to REALLY implement his/her advice. It's a lot harder than it sounds.
- It can not be overemphasized how much you have to rest and go easy in the early stages. If you are going to practice an hour, at least 30 min of that should consist of rest. DO NOT whip yourself into working hard early on, it will be counterproductive. Seriously. I was very dumb when it came to this. I thought I could beat difficulties by working super hard. BIG MISTAKE. That actually held me back and I am convinced that it slowed my progress a lot. I've had a different approach restarting a few months back and the results are very encouraging. It is possible to practice 2, 3, 4 or more hours per day (if you have that kind of time) ONLY after you have acquired the means to do so. Trying before that will just keep you from making any progress or destroy your embouchure altogether.
- Develop awareness of your body and breathing. Maurice Andre said: "With the trumpet, everything is interior." Playing trumpet is kinda like a form of yoga. It demands a keen understanding of your body and constant awareness of what is happening INSIDE of the wall formed by your lips, from your aperture, jaw, tongue to the relative position of your hips and spine. If any part of your body is not participating in effective sound production/modulation, it is likely getting in the way. This may be a more difficult thing for some teachers to convey. Since they learned as kids and practiced many years, some things are instinctive to them and they don't even realize they're doing it.
- Visualize: your aperture, the muscles forming it, the sounds produced, air in your lungs and airway etc...
- DO NOT get into fights with difficult exercises, tunes, pieces, or single notes. They'll always win. When you run into something that you can't play or can't play well, that's because it's above your level (duh!). Your level is not going to change at that moment. Working on it will improve your level but at that given moment, you WILL NOT get it right, no matter how hard you try. Bits and pieces yes, the whole thing, not a chance. The harder you try, the more damage you can do to your embouchure.
- Discomfort is a warning sign: you're doing something wrong.
- Start exercises at slow tempos, then polish them at slow tempos. Once you really have it, you can go a lot faster/cleaner than if you try to accelerate progressively. Don't worry too much about speed, adult learners have many more ways to make music than seeking virtuosity, which is a VERY remote goal for us.
- Most important and most difficult: don't obsess on range/high notes. Range WILL inevitably happen on its own IF you do everything else right. Down the road, once you have the means to work on it, you can do specific range increasing stuff if that's what you're into.
- Play with others, because that's what it's all about really. Duets with your teacher or other players of similar level are challenging and fun. Study both parts of duets, record yourself playing one, then play along the other part. Even with crappy equipment, it's worth doing. As soon as you can, start playing with a band, make it very clear what your situation and abilities are. Often times, adult players are, by default, considered to have better than 8th grade abilities (although I'm not entirely sure what 8th grade level is like).
- Read what Rowuk writes here, he knows