When marinating don't use a plain steel or aluminum container to hold your food. Prolonged exposure to the aluminum can discolour your meat and give it a slight metallic taste. Use ceramic, glass or stainless steel containers whenever possible. Many use the resealable freezer bags for marinating and these do a wonderful job as they allow you to expose all the meat to the marinade.
Marinate in the fridge. The acidic elements of your marinade (juice, wine, vinegar, etc) do not require warm temperatures to do their job of breaking down the proteins of the meat you'll be grilling. So follow standard food safety procedures and keep your meat in the fridge until an hour or so before grilling. 
Almost any marinade works well as a finishing or dipping sauce. The trick here is you need to boil the 'used' marinade for at least five minutes to eliminate all the potentially harmful bacteria it might have picked up from the meat it's been mingling with lately. When boiling keep an eye on things. Marinades containing lots of sugar can go from liquid to a sticky solid very quickly if you're not careful. Once your marinade is boiled and safe, you'll be amazed at how much flavour it can add to your food post-grilling.