Acid: Wine, vinegar, citrus juice, beer, and yogurt weaken the proteins in meat and seafood, rendering them more tender and moist. Acidic ingredients also tend to make fish taste delicate and less fishy.
Fat: Usually oil but also coconut milk. It adds moisture and helps keep marinated food from sticking to the grill.
Aromatics: Garlic, citrus zest, lemongrass, minced chiles, and herbs penetrate the surface of the meat, giving it flavor. Experiment with whatever appeals to you, from pesto to pepper jelly.
Pictured: Chicken with honey lime marinade