For my E70, since it was neglected and came with lots of oil/dirt/grime build up all over the place from various oil leaks (fixed now), some of which was very thick, I used Gunk Engine Cleaner & Degreaser Part No. EBT32 and and air powered cleaning gun. I've used many other products, but personally like Gunk.

Air gun: https://www.amazon.com/gp/product/B00ELDY936/ref=od_aui_detailpages00?ie=UTF8&psc=1

The gun allowed me to get into a lot of places a simple hose (not enough pressure or too much 'splash' effect) or pressure washer (too much pressure) wouldn't be good options. This gun let's me dial the fluid pressure back, mix a small/minimum amount of cleaner with water (or use straight solution) and get to places otherwise off limits.

For just a dusty engine bay, I wouldn't go this far. For other vehicles, I've used aluminum foil to cover any electronic/sensitive parts that I didn't want to risk getting wet and just used a garden hose with sprayer attachment and some kind of soap or degreaser depending on how clean/dirty it was.

Afterwards, put on some kind of dressing to keep all the plastic bits healthy and aesthetically pleasing, but one that doesn't attract dust.