Make sure your equipment is working properly. Check all your connections and your antenna system frequently to make sure that you are not causing interference or irratating noises on the repeater. If you are using a power supply, make sure it has the proper filtering for radio use. A power supply with inferior filtering can generate a very annoying AC hum. Try to resist the temptation to editorialize.
Nothing sounds worse than some blowhard that has all the answers, regardless of the question.
And last but not least, it takes many hours of dedication and expertise to maintain an effective repeater. If you find you are using a repeater frequently, offer to help out or take out a membership with the club that sponsors the repeater.