That's probably one of the most broad questions you could ask in music. That's like saying"I am working on living, any ideas". lol, but seriously, in what field? Give me something to narrow it down.

Get the Rubank Method blue books - all of them (Beginner, Intermediate, and Advanced I & II.) I've been playing for over 20 years, and I still use the blue books as part of my practice routine. Also, get Rubank's "Selected Studies" book. All their books are inexpensive and jammed full of exercises. The blue books even have a lesson plan built into them so you can help yourself along. These are not Jazz books, per se, but great for improving your technique. The Selected Studies book has two studies in every key - major and minor. These would help develop technique and ideas that you might apply when playing jazz or improvising. Private lessons are also the way to go. Not that you can't become a great player without them - it just helps if you're looking to improve faster than you're currently happy with. I might start taking lessons from one of Larry Teal's students before too long. I'm good enough for what I do currently, but I'd like to get to the next level.

Thanks to everyone who responded and stuff. I am mostly looking into Jazz improving. I will hopefully be taking some lessons this summer from a guy I know who plays bari professionally in New York. I actually have two of the Blue Books and I like them too. I will probably start using them a bit more than I have been to help improve. I`m already ahead of most players my age, so I`m in no big hurry to get anywhere fast, just gradually improve over time. Thanks for any other ideas you have.

Do long tones and aim at getting a good sound. This is something you can do on your own and it will strenghten all parts of your playing regardless of your level of development.