Engine de-greaser on a warm(not hot) engine(flammable so be careful around exhaust, and don't start car until completely washed), should be your first stage. Bring a toothbrush and/or new toilet brush, and wear eye protection. Use lots of cans before you add water. Once you add water, the gunk that's on there that is not scrubbed off will take 2x more scrubbing to get off, so scrub hard before you rinse. I heard dollar store tooth paste and a clean hard (human) toothbrush works wonders for detail on things like unpolished aluminum, and hard to get spots (don't use on polished surfaces).
If you use high pressure water cover anything that might not like high pressure water.
I'm sure others can chime in.
Found another methodology wich is probably safer, but will use a little more elbow grease, and pocket change:
http://www.autogeek.net/engine-guide.html
Another guy has had success with scrubbing bubbles!!:
http://www.m5board.com/vbulletin/e63-bm ... y-way.html
Oh and if you want to save money instead of using engine dressing for plastics, use cheap new oil. The dealership I go to uses cheap hd-30 oil to dress up the engine bay. Don't use it on hot parts. But it seems to attract dust just as much as any other engine dressing, looks the same, and will cost way less in the long run.
You should probably use wax on the body panels though.