Run the dry oats through a food processor to break them up.
3/4 cup old-fashioned oats
In a large bowl, combine oats, ground beef, tomato juice, egg, onion, salt and pepper, and mix well with a fork. Press firmly into ungreased 4 x 8 inch loaf pan.
Do not overmix your meat mixture, doing so will make it tough. Mix just until everything is combined. Try not to smash or compact it too much.
I prefer 85/15 for meatloaf. You want some fat for juiciness and flavor, but not too much that it's a greasy mess. 80/20 will work as well, as the fat melts during the cooking process, helping keep the loaf moist and tender, not dry and crumbly. In addition, meat with too high of a fat content will shrink, a lot.
I use a meatloaf pan with a drip insert. If you haven't heard of one of these, and you like to make meatloaf, you should have one. It's basically an 8x4 loaf pan, but there's an additional insert pan with drain holes that you place inside the main pan. The meat cooks in the pan with the drain holes, this allows the fat to drip down away from the meat, landing in the pan below. There's one at Amazon here, I've had mine for several years.