Only use a pressure washer on its lowest setting! if you have the water pressure too high, you can force water into electrical connections etc etc.

Hose pipe with one of those adjustable nozels will do as good a job and most have a setting for delicate watering of flowers, which will work well as a wash down.

When cleaning, make sure the engine is cold... this means the products used don't dry to fast prior to breaking down.

Cover things like Air filter, MAF, Alternator and battery terminals.... tin foil works well

You can buy a cheapy steam cleaner with a small nozel attachment that will do the same job and will allow you to clean specific areas at a time...use a microfibre to catch the dirt as its blown of and dry as you go.... more control over a pressure washer.

You can use silicone engine dressings to enhance the clean, both for engine and plastics. The engine dressings work well at sealing electrical components too



You can do it all 'by hand', just use a damp cloth for clean up will be a lot more work over entire bay though