I use a few stages, but easy to do. Most important, don't clean the engine when it's hot, everything evaporates instantly and doesn't have time to clean or get rinsed off.
1. Blow out any dirt dust, my car wash has a blower system which is great. I find dirt likes to hide out in the pulleys.
2. Wet down with low pressure spray
3. Simple Green spray bottle the whole engine bay, hoses, heads, valve covers, everything. Let it sit for 5-10 minutes
4. Rinse eveything out with the wash gun, the only thing I try to avoid spraying directly is the CAI filter and electronics module on the passenger-side firewall but if they get wet it'll be fine.
5. Liberally spray a protectant, I use mother's protectant spray for the engine bay, but the CD2 is a great detailer as well, I just can't find it out here. Let sit 10-15 min.
6. Wipe off the excess protectant with a microfiber cloth.
A good tip is to do it regularly, because maintaining a clean engine bay is a hell of a lot easier than trying to clean it up everytime. I normally just rinse the engine bay every wash then detail it for shows.