My advice to you is to just open up your throat and make sure there is lots of air going through your instrument. Also LONGTONES. everyone hates them because they are so monotonous and boring, but if you do them right, then your breathing will get better and so will your tone. If you don't know how to do longtones, this is how. YOu should probably play into a wall so you can hear your town. First you should pla the lowest note that you can. Make sure you have good airsuport and posture. HOld this note as long as you can. Try to work out problems there. THen go chromatically up the entire horn. Do these every day and your sound will imporove dramatically.