First, there are three ways to be approaching this.
1. You may be replacing someone that was highly disliked and not respected by most/all. Or you may be replacing someone that was highly popular in the community. Or you may be replacing someone who was polarizing (liked by some but not by others). Or you are replacing someone who was (to be less than polite) forgettable. It is always wise to see what is going out the door while you are going in. Learn what you can to not fall in certain traps.
2. Once you get started building relationships is your first goal... can't overemphasize this... build them with your colleagues, students, staff, booster organization... get to know names and faces.
3. Don't try to change all things at once. Especially if you are replacing someone who was liked or highly thought of. Earning trust and building community in your organization is more important than immediate enforcement of your policy ideas. Think of it this way... you must go slow before you can go fast.
4. Don't put too much pressure on your self. You will feel it in the head position and you have to find ways to share the load. You must be organized and you must be diligent, and you will probably spend more time at the band hall than you did as an assistant, but realize progress and growth in an organization take time. The seeds of the band that you will get next year were planted years ago and it will take time for that organization to really have your true thumbprint on it.