Make sure the fuse box and battery cover are on and secure avoid hitting them with direct pressure, try not to hit the alternator if you do a little not really a big deal you just don't want a lot of water exposed to it to prevent anything from corroding... everything else is water tight enough for just normal hose pressure. As long as it is not very cold water/outside temps I'd do it on a warm block so it helps it dry I recommend using just simple green as it is environmentally safe non corrosive and non flammable also not harsh to plastic like other degreasers it will give you more piece of mind. let it soak in for a bit and use a brush lightly on non metals obviously, and let dry adequately before driving, that does the job for me.
I've cleaned several & I've not covered anything... Chemical Guys has some good videos also. Cool, rinse (no pressure), APC and brush in with detail brushes, rinse. I use a air compressor w/ a small tip to blow out air in tight areas. Then a nice dressing that I let soak & brush in again & then wipe down with a clean microfiber towel.
I did it in my Mustang recently and I have an open air filters. I just stay away from a lot of water & it was fine. Basically use common sense.