A great way is by charging for volume of trash produced. My city works that way (pay per bag) and we produce very little trash (sometimes not even filling a trash bag in one week). It also makes you really consider buying something when you include the potential cost of throwing it away, if it is not reusable.
I understand where your coming from. If you are used to cooking “by the seat of your pants” for one scaling to a group is more complex than just increasing the amounts.
A couple things that can trip you up:
Prep: Bigger ingredient amounts mean you probably should prep them before starting. E.g I can peel and dice one potato in the time it takes water to come to a boil. 6 potatoes, not so much. Do a mise en place.
Seasoning: taste more often and consider aiming for a more “average” palette. E.g I like my food with very low salt but more pepper, but I don’t do this when cooking for others.
Pans: larger sizes mean you might have to do some steps in batches (browning) or use two pans where you could have used a single pan for one (e.g. split the pan and brown meat at the same time as cooking onions). Create pans/trays to hold the parts of the meal that are partially cooked. When making a lot of something, a little prep and organization makes things go smoothly since you might be repeating the same task several times, so if that task is a little quicker, you get a big benefit. Whereas you might not want the extra prep pans to wash when cooking for one, when cooking for more the better organization actually makes it go quicker.
You still can cook by taste/eye/instinct for the ingredients and amounts. It’s just that planning and organization becomes more important.