I find meal planning to be the easiest thing all together. I'm very organized and I'm TERRIBLE when it comes to eating on the fly, because that's just not how my mind works.
If you go to a calorie calculator to find out roughly how many calories you need to lose
Like This then plan out your meals, it's kind of like balancing a checkbook. Weight watchers works the same way, but instead of calling them calories, it's points.
For example, what I do is list out for the following day my breakfast, snack, lunch, snack, dinner, snack and allocate calories (or ww points, or other units) to all of them and add them together for my total.
Eventually you have a better eye for estimating calories for foods that you're used to eating. What makes it even easier is cooking meals and freezing them in portions with calories/points/units labeled on them (you can find recipes with nutritional info online). Then you can say to yourself, "I'll take out that particular meal for tomorrow's dinner" and there is no further thought required.
Not only that, it's a lifesaver on busy days!