It all depends on the flavor profile you're going for. You'll want some salt, a little sweet to enhance flavor, some spices, and a little acid.
Put some chopped garlic, minced ginger, a shallot or 1/4 red onion in a food processor. Add a dash of soy, some lemon or lime juice, and a pinch of cayenne (hot) or more of ancho powder (not so hot), a pinch of sugar, a dash of apple juice, and 1 Tbsp Worcestershire sauce. Marinate the meat for a few hours in this before grilling. This is similar to Stubb's beef marinade, but it's a good start for any meat heading for the grill/smoker. You can add a rub on top of this if you want, just before smoking, but for grilling, it may be overkill. Good luck.