Two other big don'ts.....
1. - DO NOT just hose under your engine bay. There are plenty of areas that water can gather and normally with some sort of cable running from it that goes into a connector. This will either cause an immediate problem or get into the socket and rust the connection. You don't want either to happen.
2. DO NOT use foil. It is not designed to repel water and IS designed to conduct electricity! Adding metal in there, with water will add to the risk of arcing between bits of metal.
Use cling film, where you can wrap it around the connector and use a watering can to rinse it
Suggest a range of brushes from alloy wheel brushes to toothbrushes for the various bits, and a few rags to wipe things clean. To dress, something like AG Vinyl and Rubber Care is good.