Sound quality is the difference between a successful band or artist and the vast majority that makes up everyone else.
You can generally count on playing in rooms that sound bad, low ceilings, parallel walls, hard flat surfaces, shared electric services, the weather, the people. These are things you have no control over.
Now consider the things you do have control over. Instruments, amplification, PA systems, microphones, cords and wires etc. Better equipment and instruments will go a long way improving your sound but getting the best sound possible with the gear you own can be achieved understating this one simple principal. How you set up your gear and PA.
If your audience can't see your speakers they can't hear them.
What they do hear is reverberant sound. Sound that bounces around the room. Before it reaches the listeners ears it has an enormous loss in high frequency content, a delay as frequencies bouncing off different walls that reach the listeners at different times. And one of the biggest sound killers of all low frequency build up.
When you set up you should walk around the entire room and you should see the speakers (paper) at all locations in the room. This will enable the listener to hear more of the direct sound over the reverberant sound and will reduce the bad things mentioned above. It will also help keep the band levels down if they are exposed to more direct sound opposed to reverberant sound.
Spending a little time on this subject will have a huge impact on the listener’s experience.