I find the simplest way is the beer can chicken recipe. The beer (or soda) can makes for a good roasting rack and eliminates the need for a rotisserie.

Put some vegetable oil on your bird and season it up however you want (start with store-bought poultry seasoning if you're not sure how to create a "rub", or use the internet-thingy to get a decent "rub" recipe).

Pop open a can of beer (or cola), pour out about 1/3, then stick the can into the cavity opening so your bird is "standing" upright. Put this on your grill and cook low and slow until done. I've never had this technique fail to yield great results.