Marinades 101:
Basically, when you deal with marinades, you're looking to employ a direct fire solution on your meat. (I know, I know: I just came back from slow-cooking a leg of lamb with a simple garlic-rosemary rub and some red wine in a "marinade" approach).
It comes down: you've got to choose a munition suited to the meat.
It's about two factors: protein and fat.
When you grill, the protein firms up and the fat liquefies. If you've got a lean cut (like a sirloin steak, for example), the protein in itself can end up pretty tough, and it requires some working over. If you've got a nice cut ("New York" strip, T-bone, Ribeye), with some good marbling (here's where select, choice and prime matter -- it's all about how well the fat has penetrated the meat. You want thin bits of fat in there. Sure it'll go to your gut, and your heart, but that's what makes it good), you don't need as much time.
What a marinade does is use its acidity to break down the proteins (making them more tender) and its flavorings to deposit flavor in the fat.
So, the fattier the cut, the less time you need to do marinade it.
Also, be very careful what you buy. "industrial" cuts, like say hormel pork, are injected with phosphoric acid to make it artificially tender. You can recognize these guys, because they've been overmarinated with a flavorless acid. They're "tender", if by "tender" you mean "spongy".
So, rule of thumb: for direct fire (indirect fire applications is grilling 201) some pieces need 12-24 hours of marinade, others (the better cuts), shouldn't be subjected to more than a couple hours. Even so, a sirloin steak marinaded for 18 hours can make you the king of the tailgate, where a raw T-bone won't raise an eyebrow.
Now for the marinade:
Remember: acid and flavor are primary concerns. A secondary concern is something syrupy -- sweet, but not overpowering -- that will caramelize under direct fire and give you a nice charred flavoring.
So here's a simple one for you: lemon, lemon peel, red wine and honey. That's your acidity and acid flavors. Throw in a single spice (rosemary's good), and garlic (nothing's good without garlic).
Here's one I use for steak (marinated for hours before hand) and mushrooms (bamboo skewer them and marinate for 30 minutes tops):
soy superior sauce --- get this in your asian food store, it's the 80 weight of the soy sauce world; sort of a combination of soy sauce and molasses.
Sriracha pepper sauce. Hot pepper sauce preserved with a flavorless vinegar. Again, asian food store. The best stuff is made in Rosemead California. If you haven't encountered this, you should get to know it. This stuff is the best hot sauce I've seen. Pure pepper punch, no vinegary or chemical flavors.
Lemon Juice
Lemon Zest (juice the lemons, then scrape the edge of the lemon peel off)
Ginger
Garlic
Peanut Oil
Onion
Puree that stuff, let the steaks sit in it, and damn if it ain't good.
Direct-Fire Grilling tips:
Get the grill HOT
sear the meat: slap it on the grill on one side for about 30 seconds to seal off the pores on the meat. Turn the meat over and let it go. The "rule of thumb" for getting a steak rare is that it should be the same tenderness/firmness as the meat between your thumb and forefingerwhen you close a fist. In practice, you grill a whole mess of meat, and you know when it's ready.
and sheesh -- stay away from that Floramo's marinade -- Ketchup is tomato sauce and sugar; Coke will just give a sugar flavor to things, ITalian dressing is crappy oil, crappy vinegar and sugar. Processed foods are to be dodged. If you want to do the same thing, use ketchup (as much as I loathe it, ketchup is tomato acid, vinegar and sugar, so in moderation, it can be applied), avoid the coke, and apply olive oil. I said a little bit of sugar -- which caramelizes on the outside. Honey is good for this. A lot of sugar kills the flavor of the food. Everybody, from church-group potluck fiends to pretentious chefs, uses sugar, and it's inevitably to hide the flavor of an inferior cut of meat. If you're grilling, bring your A-game, and bring your A meat. There's not sense going to battle with a dismal cut.
