Does following the serving size help?

Depends on the food and the listed serving size. Some serving sizes are pretty small if you take the time to actually weigh or measure them out as listed on the package, and don't give you much food for the calories listed. Other things, like chips, I've found that I can weigh out a half serving onto my plate with a sandwich and be perfectly satisfied - but then I don't eat chips for their nutritional value, but because I like 'em!

I pay attention to serving sizes for calorie count purposes, but I also go for the most bang for my buck with the calories I eat - protein, fat, carbs, nutrition in general, really, and if the food is going to keep me satisfied for a long time. And of course if it fits into my calorie goals.

Definitely read your labels, both servings sizes, nutritional info and ingredients, and log things as accurately as possible. Logging is an excellent learning tool - look back over your days and weeks and see where you did well, and see where you could do better - was a serving size enough, or would 1.5 servings be better, and still meet your goals? Was the serving of Foot Loops worth it, or would a different breakfast or snack have been a better choice? It takes time, but it's worth, and soon what to eat and how much just becomes second nature.

I started this process by following serving sizes-it was an eye opener to see what a portion actually looks like, and it made it easier to count calories so you're not having to get the count right for like 2.3 servings of something. On the feeling full issue...feeling full depends on volume of food in your stomach, initially, and then a little while later on what macro nutrients you ate as they begin to be digested. We can't go by volume of food-some is calorie dense and some is not. That's the big secret-it's not amount of food, it's # of calories. If you feel like eating a lot is necessary, then lettuce and veggies will be your friend. If you'd rather eat rich prepared foods, you'll have to make peace with the small amount you get in a serving. Spaghetti is my favorite food... It was a shocker to see how small a serving is for a reasonable #of calories. Now I know why my mother never served it without a giant salad appetizer. It kind of sounds like you're not counting calories yet-because you can't do it without measuring your servings. If you're not ready to try that, then yes, it's still helpful to measure out servings so you know what's a reasonable amount to eat of different foods.

+1 Total calories are what matter.

I don't really care what the bottle lists as serving size. If I eat more or less of it, I just make sure to weigh it and log the right number of calories by weight.

I think serving size was originally intended to be an easy way for people to look at a label and guesstimate how many calories they'd eat. But food companies have been so manipulative with unrealistic serving sizes on labels (0.5 second spray, really?) that it's almost moot.