One key I have found is never car wash it,the soap they use at a car wash is hard on paint,I hand wash mine with a mircofiber rag and always wet,don't dry rub it.
Also I don't wash it unless its real dirty/dusty with bugs,I use a spray detialer and clean it that way,a detailer will actually lift the dirt and scratch when you wipe it.

oh yeah the deepest,darkest black I have found is dupont hot hues blackend looks great