Quote Dave Gate:
Nowadays very little, short tail, mainly on vocals.
I agree, as a 'default' position. But it really is a case of knowing what each of the controls does so that you can apply the appropriate effect to enhance rather than muddy the sound. I practice with some simple solo sounds - eg. 'dry' vocals, dry acoustic guitar etc - just to determine exactly how each control alters the sound. Eventually, you'll do it like driving - without thinking.
... and if anyone in the audience can say, "Ooo, reverb..." you're probably using too much. Of course, some styles of music go hand-in-hand with a definite and pronounced reverb/echo sound, but I don't think that's what you're asking...