Cover all electrical components of course, but be particularly careful about the spark plug wires/boots. They are not watertight, and will cause starting issues once wet. Might want to keep qtips and/or pipettes with you that can reach into the bottom of the plug wells and soak/remove the water. I would probably use masking tape or a shop towel to protect them, tough though for the rear bank.
You want the engine bay warm, but not hot. Should be able to touch the engine without a boo-boo. Use low-med pressure only, think of it as coming out of a garden hose or a "SHOWER" setting on a hose nozzle. If you see obvious sedimentation, work your degreaser into the dirt first with a paint brush or something similar, before hosing down the engine bay.
