Any suggestions?

Getting quality private instruction is probably the absolute best thing you can do for yourself.
Have an experienced player play your horn to make sure it is really in good repair. If it's not, get it in the shop. It's hard enough to play without a dragging slide.
Practice well. Know what you want out of each practice session, not just noodling. Practice things only as fast as you can play them right. Then work the speed up. The constant need to move along faster than we should is a huge killer of fundamentals.
Listen to lots of music and listen to lots of bone players so you can get an idea of what you want to sound like.
Play music with other players. Have fun.
Again, quality private instruction is the best thing you can do.

I MADE FIRST CHAIR!!! AND THANKS FOR THE LAST TIP!!!

Congratulations! Keep practicing!
Funny thing about trombone playing (and music in general)... The more you learn, the more you'll realize you still have to learn. It's a lifelong journey. Don't let the first chair thing go to your head. Just keep working on getting better.