I always read labels, now.
I look first of all to see if any of the fat is trans-fat. And I don't just look at the box that gives grams. I go straight to the ingredients to see if there is any hydrogenated or partially hydrogenated fat in there. Because they can put it in and if it is less than a certain amount, they can say zero trans-fats. It may be a very small amount, but that stuff builds up in your system, so I just stay away from it completely.
I look then to see what the sugar is. Is it high fructose corn syrup? Is it refined sugar? If I'm going to buy something with cane sugar in it, I try to have it at least be unprocessed, like cane syrup. Better yet, I look for things sweetened with fruit juice or honey.
If it's sweetened with cane sugar, I also look up in the other box to see how many grams of sugar per serving. I personally don't even look at the calorie box or fat count. I care more about what the source of the calories is and what kind of fat it is.
You may care about other things like salt content or maybe you do care about how much fat there is. We all have different concerns.
When I am buying something like cereal or a frozen pizza, I look to see how many ingredients there are. Some lists go on and on! Next time you are at the store, grab a frozen pizza, and then grab a Tombstone pizza. Tombstone has very few ingredients by comparison. It is made of the things that a pizza should be made of : flour, yeast, salt, cheese, tomatoes, etc. The other pizza will have a huge list of things you don't even recognize!
Some of the things listed are vitamins and things like that. You could look some of the things up on line. Other things are preservatives and additives and junk and fake stuff.
I think label reading is a good habit to get into. It takes some more time, but at least you will know what you are eating.