I'd advise you not to use a pressure washer. It's completely unnecessary. A garden hose will suffice.
Cover any electrical parts with a plastic bag or something similar. This includes fuse box, ecu, air intake.
Rinse your engine down with water, and then spray some degreaser to get off the tough spots. You don't want any concentration of degreaser cuz it will stain the metal parts. For those really bad spots, you can use a brush to loosen the dirt. Rinse it off, and start your car right away. It will dry up any water where you don't want it.
Worst case scenario is your car won't start cuz something got wet that shouldn't have. Just wait for the car to dry up, and try again.