The biggest concern is to not get any water down where the spark plugs are - the water will just sit in there and kill the coil packs.
Basically clean everywhere but not the coil pack areas. Just use a cloth and spray cleaner - I actually use a window cleaner spray, because it evaporates quickly and you can work it around the coilpack area without worry.
Otherwise depending on how dirty the other bits are, it'll be a mixture of elbow grease, degreaser, brushes, cloths, water, pressure wash (steam or very hot setting), and finally a decent plastic shine like Aerospace101