Think of a marinade recipe as being like a salad dressing, it acts as a seasoning and adds flavor, but gets an extended period of time to do it's job.
For a Mediterranean style marinade take equal measures of olive oil, balsamic vinegar, mix in a little mustard. You could add some chopped rosemary, or oregano, salt and pepper, garlic.
For something more acidic, substitute the vinegar for lemon juice and grated zest. Note that oil, acid, seasoning and some other flavouring (a herb usually works) are all things that could go in a salad dressing.
The trick is to keep it all balanced, don't put too much of a favourite ingredient in. Given the sheer number of flavorings that can be used in a marinade it follows that there is a lot of scope for experimentation.
A whisk comes in handy for mixing along with measuring spoons and a measuring jug.
It's worth pointing out that a copper or aluminum bowls for mixing or marinating will leave a nasty metallic taste. Always use a glass, ceramic or stainless steel bowls or jugs.
Some chefs use a seal-able plastic bag for marinating. Put the marinade and meat inside, squeeze out the air and seal it. It takes up less space in the fridge if nothing else.
No special equipment is needed that a household cook doesn't already have.
The amount of time to marinate depends on the meat you're using. There is no advantage to leaving it for a longer time - and the grain of the meat maybe damaged anyway.
As a rule seafood take the least time at 30 minutes maximum - beef or lamb joints can be left for 2-8 hours, or even 24-48 hours if using a yoghurt based marinade.
Below are some rough timings for reference.
Prawns - 15 minutes
Fish - 20-30 minutes
Chicken - 20-60 minutes (depending on the amount of 'acid' used)
Pork chops - 45-60 minutes
Lamb chops - 45-60 minutes
Beef steak - 45-60 minutes
Beef roast/joint - 2-3 hours
Lamb roast/joint - 2-3 hours
Pork roast/joint - 2-3 hours
As a rule of thumb a 1/4 to 1/3 cup will cover 1/2 pound of meat.
Making and using marinade recipes requires some forward planning, especially if the meat needs a few hours. You can prepare it before you go out for the day to work or wherever and have something delicious when you get back.
Always refrigerate meat if it needs to marinate for a period of hours.
When you come to grill the meat, use any remaining marinade to baste it with - this will really add extra punch to the flavour.
Never consume raw marinade if it's had meat in - if it's used at all, it needs to be cooked like anything else.
If you're not sure, make some extra and set it aside for basting.