I cover the visible plugs and elctric leads with regular shrink film from the kitchen, spray on a good-quality engine cleaner (I use Autoglym but I'm sure Zaino got it as well). Then I use my pressure washer set at low pressure and use it from a little distance. After that I use a soft brush to loosen dirt in the tight spots. One more careful treatment with the pressure washer and a gentle drying with an old cotton towel. Once or twice a year I also give all the plastic covers and panels a spray with plastic & rubber care spray and leave to dry.
I have been doing it this way with 4 cars over the last 5 years. Never had a problem but sure do have a clean engine bay most of the time