First off, the above is just a guideline. Season it to taste, and the amount of wet vs. dry that goes in will vary a bit. More on that later.
If you are going to use store-ground beef, I recommend getting the market ground (in-market, using scraps). That's going to be the freshest and most tasty. Of course, I recommend doing the below - grind your own.
If you are using a more fatty grind, you can use 2% milk.
Grind the beef (skip this part if using pre-bought).
Assemble the meat loaf
This is where it can vary. If you want a really thick, dense loaf, go a bit lighter on the milk and some of the other wet, and put less bread in. If you want the meat to go farther, or want a lighter loaf, you can keep adding a balance of the wet and dry ingredients.
As I said, this was a basic Meatloaf. You can add just about anything. I like a small amount of finely chopped mushroom and a bit o corn. You can use barbecue sauce to spice it up instead of Ketchup, use Italian bred crumbs instead of plain, use different kinds of meat, like Turkey, and chance the spices to whatever you like.