1.) Locate either some engine degreaser or cleaner from a local auto parts store.
2.) Open up hood, and with the car off, begin spraying down the motor with the degreaser according to the directions of use on the bottle. Some cleaners may say aviod contact on plastics / hot metals to prevent material discoloration. ** DO NOT make contact with the ignition coils and the Electronic Controlled Module (ECM). ** Also, if you own a DOHC [LQ1] is recommended to duct tape the spark plug boots so water does not seep into the deep access hole.
3.) After spraying down, let it settle in for a bit to have it break up the old sludge / dirt that's collected on the motor.
4.) Once time has pasted, locate home hose or power-wash nozzle at a self-serve car wash (highly recommend for best results) and shoot the motor to remove degreaser and dirt / grime / sludge. ** Again, avoid prolong soaking of the ignition coils, ECM, and also the gaskets. Yes, they can get slightly wet, but don't hold the water pressure against it. You could have problem with starting the car back up. **
5.) Once washed off and suds / degreaser is rinsed away, let car drip dry for about a couple minutes. You can, if desired, to towel off any parts of the engine, just be careful about being burned (if car was running previously) and moving parts.
6.) Start car and double check spark plugs for no arcing of spark to block. Give the engine some RPM's to make sure the serpentine belt is not slipping over the accessory pulleys.
7.) Drive away to you next car show or your buddies to show that you DO have a motor underneath that hood of yours!