clean
if it's clean and just dusty I just take the water hose and set it to a fan spray and hit the whole compartment lightly then take my air hose and air off everything I can touch. Start the engine so the heat can boil off all water on or around the motor.
If its real dirty, I take simple green at about 50% and spray let soak for a few then take a paint brush and hit everything in site then spray off and dry. Do this before you wast your car. You may want to wax around the front end and the simple green may remove any wax. My engines are always clean, I never use anything to make it shine, I just keep it looking original.
Once a month you should take a wet rag, water only, and wipe down everything you can touch. Use simple green where needed.