Outside of a few choice Black Eyed Peas videos, lumps are rarely associated with something good. When it comes to making sauces and gravies, nothing causes performance anxiety in an inexperienced cook like these malevolent masses. The good news is there's an incredibly simple way to prevent lumps.
Repeat after me, "Hot roux, cold milk, no lumps." That's it. As you'll see in the video, no matter how sloppy your sauce making techniques are, as long as your liquid is cold, and your roux is hot, lumps are almost impossible to create. Below the video, I've given the ingredients for the simple white sauce I used to illustrate my point. I turned mine into a beautiful macaroni and cheese, but this has so many other applications that mastery of its silky-smoothness is mandatory for any wannabe cook. Enjoy!
3 cups whole milk
4 tablespoons butter
3 tablespoons flour
salt and cayenne pepper to taste
pinch of freshly grated nutmeg
1/2 teaspoon fresh thyme leaves