Playing music isn't just about playing your own part. It's also about listening. When you play in a group, don't focus on your own part. Listen to the entire ensemble and you will hear yourself in it. If everyone does it, the group will automatically sound better. When I conduct small groups, I tell the students to do that. It's amazing how the intonation and ensemble immediately improve.
Don't be just a good player, be a good listener!
I am associate principal horn of the Singapore Symphony Orchestra and the author of the progressive methods. I'm happy to share my experience as a horn player and teacher with you.