Easy stuff.
1.Booze. In fact this may be all you need for a good bbq.
2.A BBQ. This is actually easier than it sounds. Often you don't actually need a fabricated grill or hibachi. In a pinch, an old barrel, or a steel jerry can, or even a dug out pit in your neighbours backyard.
3.Even source of heat. This is very important for the success of your bbq, because if the heat is not even your meat will not cook properly. Charcoal is an excellent source of heat and can be made by slowly burning logs in a seperate fire, then transfering the charcoal to your bbq apparauts. Or it can be bought from the store your stolen from your neighbours yard. I don't suggest burning petrol or other things under your meat as it imparts a sickly taste and it's difficult to control the heat.
4.Meat. Now whatever preference you have towards meat, the result should always be the same; juicy and tender, tasting nearly like butter with every bite. So here is the trick. Buy the fattiest meat you can. Your steak should be marvelously marbled with fat, your chicken should be plump and squishy. Seen as how I don't eat pork, you are advised to consult someone else. The second most important thing is to age your meat. The best way to age your beef is to put it into a spot where flies won't get to it and let it get ripe. Not so it smells bad, but just enough it will get grey around the sides. In the refrigerator this may mean two weeks, on your patio or garage this may mean several days. Just keep it away from direct sunlight and any overly hot places. Chicken is the same, only significantly less as chicken goes bad very quickly. So stay on it and be careful. The other popular way is to create some form of marinade and leave soaking in it for several days or weeks. This method is quite good, although can be messy.
5.Patience and experience. This is most important thing when bbqing. If you are able accomplish this, then nobody will be able to beat your meat! So when you are bbg your meat, don't turn it until the side is finished. You should only turn it once. Depending on the size, quality and rarity of your meat then you you will keep it on longer. You can adjust your heat partway through, so pay attention to that. If your meat is on wood or bamboo skewers then remember to soak the skewers beforehand. Just use your common sense. If your meat has been hanging from a hook in your toolshed for a week, then you may want to cook it through. If the meat was freshly bought from the store only hours ago, then you can leave it bloody rare. Just remember that we are hardy creatures and we can take more than we think. Happy BBQing!

I had a really nice rack of ribs cooked at a BBQ which had two types of grill made from steel barrels.

The simplest, was used to cook the ribs. In the bottom of the barrel, they dumped a big bag of charcoal, lit it and let the heat even out. Then rebar pieces were laid across the top of the barrel and the cook, applied dry rub seasonings to the meat. Next, he used hooks made out of what looked to be pieces of wire coat hangers, to hook into the top edge of the rib racks, and hung them evenly spaced inside the barrel on the rebars. Put the lid on, and wait awhile. He may have had an exact timetable, but that is up to your culinary discretion.

The other BBQ was dubbed the Ghetto-Q and consists of a barrel on its side, torch-cut in half, hinged, which opens up like a huge post-idustrial clam shell. Inside it has tradional oven style grill racks, and a few inches below that, a metal mesh (looks cut from fence material) to keep continuity of separation between the cooking fuel and the food. The whole thing is attatched to a heavy rolling table-frame. To make, it of course reqires some metal cutting, and perhaps some welding, depending on your construction ingenuity.

I also imagine a good base for a BBQ would be, the bottom section of a barrel. A fitting lid could be made from the metal in the top section.

Happy flaming.