I take my car to a touch-free gas station wash near my house... Then hit it with detailer spray and a soft microfiber when I get home. May not be the absolute best approach but it takes very little time.
'08 E90 M3 - Alpine White - Sold
'13 E92 M3 - Silverstone II - Sold
'04 E46 M3 - Jet Black - BBS E88, KW Clubsports, Brembo BBK, SuperSprint Exhaust, Recaro
'15 i3 - Laurel Gray - Why would I mod this thing?