You will get several GREAT posts on this subject. This one is my opinion, but has served me well in my later years after struggling at times with this subject.

1. Start class on time EVERY Day.

2. Have a daily routine for warm up and start playing ASAP-save announcements for end of class. The first 10 minutes are PRIME instruction time. Warm up is NOT for warm up. Warm up is for instruction on tone (enough air?), rhythms, balance, tuning, scales (the keys you see in your music), articulations and more.

3. Talk less and play more. Use the absolute minimum number of words. Have someone time your delivery. This one was a huge wakeup call for me.
Are you talking more than playing? If you waste 5 minutes per class period, over the course of a year you are losing 18 rehearsals. [Do the math] Bottom line is PLAY don't TALK.

4. Score study prep. Find sections with the same musical line and rehearse them together. Horns/Alto Sax, low brass and reeds, Flutes/Clar/Trumpets, unisons. Find a phrase, work those 3/4 groups individually then put two together, then add one, then add the last one.

5. Work backwards a few days each week! Start with the last section, teaching, cleaning, etc. Then go backwards to the section before that....repeat AND play to the end. Keep adding previous sections one at a time and play to the end. If they know where they are going (the end) they will likely play same or similar music to beginning.

6. Don't get bogged down fixing EVERY note and rhythm at first. Commit to finishing a complete phrase, then go back and make a few corrections. Ask your students if they can "fix" one thing in that phrase on their own. You'll be surprised with the result.

7. Get those parts out of the binder sheets and have students WRITE on them. Missed fingerings, who they match with, etc.

8. PRAISE, PRAISE, PRAISE! without getting wordy. Thumbs up, smile, nod, single words like "great", "awesome", "Oh yeah", "nice", "that makes me proud"................

9. When you have to make a correction for mistakes or discipline, use fewer words. Then asap look back at that individual and acknowledge their correction. Use #8. I guarantee they are checking to see if you are pleased with their effort.

10. Choose some easy yet fun music. As your rehearsals become more efficient, go up a little in difficulty. Success breeds success.