Marinades are fantastic! You start off with just enough liquid to cover the meat, usually something like olive oil, lemon/lime juice, cooking sherry, vinegars, soy sauce, etc. Then add spices of your choice, cover, and refridgerate at least an hour. I prefer to leave it overnight so that the flavours really permeate the meat. Depending on what flavour you are going for, here are some suggestions for spices (use any combination of the following):

Tex-Mex: olive oil, lemon/lime juice, tablespoon of tequilla, chili (ancho is especially nice), salt, pepper, cumin, oregano, garlic, cilantro/coriander

Northern African: olive oil, lemon/lime juice, garlic, thyme, onion, harrisa, chili, pepper, cinnamon, ginger

Oriental: dry sherry or rice wine, soy sauce, garlic, ginger, 5-spice powder, salt, pepper

Thai/Indonesian: lemon grass, fish sauce, pepper, rice vinegar, coconut milk, chili, garlic, ginger, galangal, cilantro/coriander

Mediterranian: olive oil, lemon juice, garlic, onion, rosemary, sun dried tomatoes, oregano, pepper, salt, balsamic vinegar, wine

Indian: yogurt, curry spices, garam masala, coconut milk, chili, onion, pepper, garlic, ginger, turmeric, mustard seeds, coriander seed

Jamacian: thyme, olive oil, whole allspice, chili, coriander seed, pepper, salt, onion, garlic

I am probably missing a bunch of variations here, but it just requires a bit of experimentation. The more a meat is cut up in pieces, the better the flavour since it covers more surface area.

After marinading, bake, grill, or pan fry your meat. Extra marinade can be used to baste meat while cooking or made into sauce. Do not reuse or eat 'uncooked' marinade because it contains raw meat juices.