The best thing to do is.. tin foil over EVERYTHING electrical, and put plastic covering the firewall where the ECU sits behind, i was really careful and taped it all down.
Then take two cans of engine de-greaser (the foaming kind) and spray it EVERYWERE dont be sparing about it... i used a can and a half. Your engine bay should look like the north pole.
Then take a hose, with no fitting on the end and just let the water flow onto the engine taking all the foam with it. Oh by the way, for best results the engine should be semi hot/warm, so that all the gunk can be easily loosened up by the de greaser.
To make the black plastic peices really shine pro detailers rub WD40 onto the plastic...(valvecover, basically everything black) i wouldnt reccommend using WD40 cause it can kill your sensors. I use a product called corrosionX, its pretty expensive and hard to get, but it works well.