I use aluminum foil to cover the distributer cap, the sensors around the throttle body, and the ecu. The aluminum foil is easy to form an cover those things, it doesn't need to be watertight just enough to keep a direct blast from the hose off.
Then i hit everything with foamy engine bright or simple green or citrus cleaner or whatever degreaser I happen to have handy and then use an old dishwashing brush to scrub whatever I can reach and then let it soak for 5-10 minutes and hose it all off really well and then pull out all the aluminum foil.
Afterwards I'll clean the battery if it needs it with a baking soda - water solution and a terminal brush and then I'll clean the plug wires and hoses by hand and apply STP clear silicon spray to them to give them a like new shine. Then start it up and run the engine for a while to dry everything off.