Throwing a slab of meat on the barbecue isn't rocket science. After a few minutes, raw meat will usually have turned into something edible unless you intentionally try to ruin it (or forget it and let it turn into charcoal).
Grilling a complete animal on a rotisserie
(rotating skewer) however, is slightly different.
After checking with a few cooks, these seem to be the important guidelines:
Have some thin steel wire ready. Use it to tie up legs and other dangly parts.
Prepare a bowl of marinade with loads of olive oil in it. You'll need to brush the meat generously with this atleast every 10 minutes. If it's not glistening at all times, it will get burnt. The oil protects it.
Add spices of your choice to the marinade. Adding red wine to the mix will help the spices penetrate the meat. My mix was about 60/40 oil/wine, with lots of spices.
Expect atleast 1/2 hour cooking time per kg of meat. Mine took just over 3 hours for 5 kg.
Keep a cooking thermometer handy. When the internals reach 75°C, it's done!
Om nom nom.