This is a great question. I love planning ahead of time. There are a lot of ways to plan.
1. Ask your friends what the restaurant is going to be. Research the restaurant and plan what you are going to eat.
2. If you don’t know where you are eating decide ahead of time what you will eat or not. For example, if you want a burger then order one without the bun (or decide if you want a bun). Or decide if you want a salad to order a salad.
3. You can decide ahead of time that if you will eat if you aren’t hungry. There have been times when I have gone out with friends and if I am not hungry I will just order a herbal tea and enjoy that.