NASA staffs its organization with engineers who are completely humorless on the subject of electronics workmanship. They’re responsible for some of the most complicated machines humanity has ever produced, costing billions of dollars, brimming with high explosives, and carrying human lives. So I suspect their standards are more than sufficient for a DIY car audio installation. Fortunately, NASA offers its Workmanship Standards Pictorial Reference for free to anyone who wants to know.
The reference offers a wide array of illustrations, from the correct use of a spade connector to high-end fiber-optic terminations. The guide shows simple examples of preferred, acceptable, and unacceptable ways of connecting electronics.
You can get every series of examples as PDFs or web pages. While some of the material is way out of most people’s league, you can’t beat it as a reference for the more common electrical connections that come up in a Toolmonger’s life.
NASA Workmanship Pictorial Reference [NASA.gov]