I got the shape when I can play about 5-7 scales in different tonalities (I play major ones, since it happend that minor is the same but one third lower), know what are the stable sounds (not always though, since I forget tonality names and thus can not build major triad, but can quite easily do that if I know the tonic).
So I start improvising in selected tonality, and although sometimes I find out something quite interesting imho, most of the time it does not sound the way I want. Also I do not know about particular ‘rules’ of the music, for example like it should end on the stable sound in general and frequently in tonic in particular, i.e. do not know the harmony.
In particular I do not know the pentatonism rules. That’s what I found somewhere in the jazz improvisation book (those days I did not understand half of the words, now I believe only a third or a quarter, so needs to find the book again):
This particular image shows way too many notes in different tonalities for my small sound part of the brain to understand.
As of trumpet – with 14C mouthpiece I’m quite able to play different scales upto/downfrom trumpet 3C (aka high C) or 2Bb on piano. That mouthpiece is default with Yamaha Xeno which I play at home, while with 7C (default on Bach Strad 37 and 43 iirc) I likely will not play that high easily, so I do not count this as 100% my technique result. Playing higher than 2F is still not very stable, especially quickly and with tired lips, but I slowly move in the right direction: train the lips and breathing.
In particular I found that playing with the full breath when air comes unaltered by the throat, mouse and tongue, and only lips control it, results in much more interesting sound than when I push the air using throat. IIRC the right breathing is exactly when air is pushed by diaphragm and not throat.
Anyway, it goes pretty well from techical point of view, but creative part is somewhat miserable at this point. But its only beginning.