One trick, honestly, is to make sure you eat some fat. Fat is something that your body latches on to to say "Yes, you have eaten food, you can probably stop now", whereas your body is more likely to keep trying to pack carbs in until your stomach is full.
Also, drink lots of water, and/or eat foods with a very high water content (like watermelon). Likewise, eat plenty of fiber. Making your stomach physically fuller is another way of telling your body "OK, you've had enough, it's time to stop."
Aim for several small meals instead of 2 or 3 large ones. You won't have sugar crashes and the like, and do stupid things like grab a candy bar, if you have planned healthy snacks (like almonds or something) throughout the day.
When you are eating a larger meal, try to eat a bit, then stop and do something else, even if you know you'll have to eat more later. It can take time for your brain to get the "I am full now" signal from your stomach, so it's good to try to give it that time. Eg eat some of your dinner, then go get started on the dishes, then eat a bit more, then go water the plants or take a walk or start a load of laundry or whatever, rinse and repeat until your body stops sending you "I need to eat more" signals.
Allow yourself occasional treats, but only in small portions. If you try to say "No, I can't have ice cream for dessert, I'm going to eat fruit instead", you may find yourself eating the fruit, and *still* ending up eating the ice cream later, whereas if you let yourself have a *small* bowl of ice cream (and then only have fruit if you're still hungry), you'll probably eat less overall.
For any grain products you eat (bread, spaghetti, whatever), make sure you get whole grain. Preferably 100% whole grain.
Try to fit in some exercise. You can eat more if you burn off some of the calories, and you'll burn more calories even when resting if you've built some muscle.