If it's really dirty, and oily - or worse that oily dirt scum they tend to get - then use either Simple Green or Gunk (or similar) and let it sit 10 minutes then spray off. Be sure to wrap your distributor and plug wires with saran-wrap, or something similar - that keeps at least the direct water off the electrical items. You might consider doing the same to the fusebox, and if you don't have the big rubber cover on the starter then that too. I use a fan-pattern spray on a hose (some pressure, not a lot). Rinse - rinse - and rerinse.
Let the whole thing dry then start waxing the painted areas of the bodywork, including around the engine, radiator, and parts of the hood. You can use a one-step cleaner-wax here if you like, but I start with meguiar's paint cleaner then move up from there, just as if I'm detailing the outside of the car. I've been using Meguiar's #20 by itself or topped with #26, NXT would probably be good too.
If you want to use dressing on the rubber parts you might want to do it before waxing. I use 303 Aerospace protectant and/or Meguiar's NXT Protectant.
Once all that is done I go over any chrome parts with Flitz (if it's in bad need for it), or a lightweight maintenance cleaner like Mother's Chrome Polish (liquid).
If you have problems with water spots and need to wash the car before your show be sure to cover the engine compartment area with a sheet, and tuck it in where you can. It'll help keep a lot of the water from splashing around the hood and onto the hard-to-reach paintwork.
These pictures didn't make it into my detailing threads on Autopia last year, they're not that great - but that's how mine ended up last year when I was done.