You've probably heard that oatmeal is a super-satisfying breakfast that'll sit like a brick—in a good way—in your stomach until lunch. That's true, but only if your oatmeal is made with a protein, which you won't get from water.
So cook your oats in regular dairy milk or unsweetened soy milk. Rather use almond or coconut milk? That's fine, as both will lend a little bit of extra heft and creaminess. But since they're still pretty low in protein, you'll need another source—like nuts, seeds, or some sort of nut butter.
You might not feel the need to bust out the giant soup pot if you're making oatmeal for just you. But oatmeal has a viscous texture that's really great at forming big bubbles.
And if you use a small cooking vessel, you're pretty much asking for your porridge to spill over. And make a gigantic mess. Ditto for cooking your oats in a smallish bowl in the microwave. Bigger, deeper bowls can go a long way toward preventing a spillover.
Microwave users, feel free to ignore this. But if you're doing the stovetop thing, when you add your oats to the pot plays a role in determining your oatmeal's final texture.
If creaminess is your goal, add the oats after your liquid has come to a simmer. If you like their oats to keep their shape, add them to the cold liquid before cranking up the heat.
Whether you're making savory or sweet oatmeal, you need to add a pinch of salt. Always. Do it at the beginning of cooking, and your porridge will taste nutty, toasty, and delicious—not boring and glue-like. (If you do it at the end, then your oatmeal will just taste weirdly salty. Try not to do that.)
Not cooking them long enough
Rolled oats cook up into a dreamy porridge pretty quick. But they're not instant. They need some time to soak up their cooking liquid in order to get soft and creamy and delicious.
So let them do their thing for 5 minutes or so before digging in. Your patience will be rewarded.