I never cleaned my engine bay before and want to run a hose over it to clean off the grime and dirt, wondering what everyone usually cover up prior to cleaning?

 

Alternator, battery, & open connections with the naked eye...

 

Running the hose over it does practically nothing. You need to get in there with a thin rag and go to town on it.

 

I've typically used the wand at the car wash on it - low pressure (don't pull the trigger), and just keep it away from the manifold, fuse box, and an open intake filter if you have one. Like Soon2BEVO says, afterwards wipe it down with rags to remove the film of grime left. Plus, wiping it down will help it dry off. Speaking of which, don't just leave it parked after that, but drive it around for 20 minutes or more to help it dry out.

I've never had a problem doing that with the 6 cars I've owned, and places that work on the car comment on how clean the engine bay is.