What is the best thing to do when you go to a dinner invite?

I never know for sure what I should do when I go over to someones home for dinner for the first time. Some people over cook so you feel horrible if you don’t eat your fair share and they have a ton of left overs. Some people under cook so you eat only a little and an hours later you are hungry. The second time around I know what to do, but the first time around I just am never clear on what I should do. Should I eat a little before I arrive or should I keep my appetite wet till I get there. I don’t eat very much and so at times a snack will suffice and I’m full till the end of the evening. If I eat nothing and they have more guests than they have food, I will get hungry and a bit irritable.
How do you handle it when you first go over to someones home for dinner?