To really get you going, I can recommend an online lesson with Greg Spence. I’m pretty sure that it would be worthwhile. I can say from experience, how difficult it is to lose old bad habits particularly when you are not even aware of them. Greg picks them up in a flash, and invariable it boils down to tension in you technique. Greg will be able to give you a decent foundation on which you can develop by following the Windworks programme.
I’ve played cornet, flugel & trumpet for well over 50 years and probably plateaued about 40 years ago, and slowly declined. Having been on the Windworks programme for about 10 months now, I’m back to (I think) better than ever, and still improving, especially in sound & tone. Like everything, you have ups and downs (including Greg’s coffee moments….they’re the really good days).
I’ve found when I seem to stall a bit, a lesson with Greg gets the progress moving again. And I know from experience, that the pressure of rehearsals and gigs do get in the way of the programme to some extent, but the more you play with Greg’s method, the more it feels natural when under the additional pressure from playing with others (or even that more difficult music where you subconsciously slip back into the old tried and tested (but inefficient) habits). Persevere!