Make sure the engine is cold.
Cover the alternator, intake, and other obvious electrical pieces with plastic (I used grocery bags). Some folks don't. I prefer to take it a little more cautiously.
Wet down the engine.
Spray a cleaner on it. I use Simple Green degreaser. Let it set for about five minutes.
Using an old wash mitt, give everything a nice wipe down. Spray some cleaner on the mitt in the process.
Rinse thoroughly.
Repeat as necessary, wiping down (to the extent you can) the firewall and inner fender walls.
Uncover the covered parts and, using a damp cloth, wipe them off, too. Be careful not to touch anything that may be charged (or, don't be afraid to disconnect your battery before you begin this process).
Before the engine is completely dry, add a shine to everything. I always use CD2, though it is getting harder and harder to find it in stores (part of me wonders if it has some ingredient harmful to the environment or you...). AutoZone and K-Mart occasionally carry it, but not often at all. See, e.g.,
http://www.thehorsepowershop.com/product.php?productid=10060577. It adds a dark shine (but not too wet) that, after you run the engine, "bakes" on to lock the look for a fairly long period of time.