Here's how I do it.
Rice (half a bowl's worth, use a big bowl)
1/2 pound Beef (cut the beef into slices, you can also use beef precut for cheese steaks)
1/2 or 1 whole Onion (cut longways)
1/2 cup of dashi
2 teaspoons of sake
2 teaspoons of soy sauce
2 teaspoons of mirin
1 teaspoon of sugar
For these four spices, you can vary amounts as you please to get a different flavor.
Pour all these into a large sauce pan and cover with a lid. Put on medium heat until it simmers.
Add sliced onions, spread them out in the broth, and put the lid back on. Cook the onions until clear.
Add the beef now. You can leave the lid off. Keep cooking the beef until it's all browned and if you're enterprising skim off the fat (I'm too lazy for this).
Now put the beef and onions over the rice. If you want it "Extra Sauce" (and I would want to interrogate you. I would want to interrogate you for roughly an hour) pour in as much of the broth as you want. As >>468839 says, green onion, shichimi, and eggs are good too. Add the scrambled egg when the beef is just about done and mix it. But the best is the pickled ginger. Not the thin flat slices you find next to sushi, but ginger pickled in sweet plum vinegar. They look almost like short little noodles. That's the kind you want. Just pile those fuckers on, they have a delicious sour-sweet taste.