This is a universal marinade used in Japanese cooking. Used fresh it's great for marinating meats or fish and when cooked down, it makes a fabulous teriyaki sauce for grilled things (yaki-mono). I use this all the time and yet until today I never actually measured anything out. I tried to keep the proportions equal to make it easier to remember, it's basically equal parts soy sauce, mirin and sake then half a part sugar and some garlic and ginger.
Depending on what you're using it for (and your tastes) you can vary the proportions and of course I encourage you to experiment with different ingredients. Sometimes I'll put some grated apple or honey for sweetness, other times I'll use chilli powder or sauce to give it a bit more kick. You could also put other stuff like scallions, sesame seeds or sesame seed oil to take it in another direction.
1 Tbs sugar.
2 Tbs soy sauce.
2 Tbs mirin (Japanese sweet cooking wine)
2 Tbs sake.
1 clove of garlic crushed.
1 tsp ginger grated.
Whisk all the ingredients together and use.
You could probably make a lot of this in advance and keep it in the fridge as it's got a fairly high salt content, though it's so easy to make I'm not sure why you'd want to take up the room with another bottle of sauce.