Do you just tip a standard percentage no matter what? Does it go down or up based on how good or bad they are?

We tip based on their attitude, friendliness and if they are on top of things. If I have to ask for something 3 times, and my food comes out cold and wrong, I most likely will not tip very well. I understand people make mistakes but we can usually tell if they are genuinely trying, or if they just don't care. DH and I often leave notes on the back of receipts if we had good service so the manager can see that.