Reddit mentions of Volume 1 - How To Play Jazz & Improvise

I was in the same position as you a couple of months ago. I went through this book https://www.amazon.com/Mitchell-Trumpet-Book-1-DVD/dp/1585607193/ref=sr_1_1?ie=UTF8&qid=1511531038&sr=8-1&keywords=mitchell+on+trumpet. I found it really good as it starts from the very beginning and it took me time to reacquire the fundamentals. I then went on to Arbans and used this book as a guide https://bolvinmusic.com/product/arban-manual/. I'm also trying to learn jazz properly and have been using this as a guide https://www.trumpetherald.com/forum/viewtopic.php?t=32146 which requires this book to start https://www.amazon.com/Vol-Play-Jazz-Improvise-Book/dp/B0002J6I8M. Any other questions let me know.

As other people are saying, listening a lot is obviously really important. But here is a fantastic tool to help you in a slightly more concrete way:

http://www.amazon.com/gp/product/B0002J6I8M/ref=oh_details_o01_s00_i00?ie=UTF8&psc=1

This was the book of choice by my jazz professor, who I studied improv with. The most important part about the book is in the middle, where there are a series of increasingly complex chord progressions. It starts with 12 bar blues, and evolves into full charts. And it comes with a CD, which has drums and bass playing those changes. To me, this was the perfect way to practice improvising. Just spend an hour a day playing along with the changes, and you get rapidly better.

The rest of the book is full of common improv vocabulary, with exercises, scales, licks, etc. Study these a bit to get some of the important vocabulary under your belt. But the most important thing is just to listen to solos you like, use them as inspiration, and then practice playing to the changes. Good luck.

A good book recommended to me by a jazz trumpeter: How to play jazz and improvise.