And you don't have to "Obey!" if you don't want to. Ha! Anyway, aside from the obvious (eat fewer calories than you use), the most effective tool I know of is
a pen and paper. If you just write down everything you eat and drink every day for a week or two, you'll most likely lose weight just from doing that. You'll immediately become much more conscious of exactly what you're eating and start to think about portion size without even trying. And if you want to make sure you're drinking enough water, just write down a mark on your paper every time you have a glass of water throughout the day. So simple and super effective!