One of the best pieces of advice I can give to any indoor target shooter is the importance of tuning. Some people I know do not take tuning seriously for indoors because the think, “its only 20 yards.”
Tuning is just as critical at 20 yards as it is for long distance shooting. In my opinion, indoors is about getting the most forgiving set up possible. One of favorite “go to tuning methods,” is walk back tuning. To do this I shoot an arrow at 7 yards, and then I walk back to about 35 yards and shoot again without moving my sight. This will allow you to shoot your center shot.
If your long-distance arrow hits right of your short distance arrow, move your rest to the left and vice versa for the opposite side. I personally have never been able to paper tune with a bullet hole. This walk back tuning method has always produced a straight flying arrow for me, which will be more forgiving under pressure.