Years ago i made 2 very exhaustive checklists...one for interior and one for exterior. And i mean exhaustive where i sat and thought of every thing i could possibly do to a vehicle both inside and out. I then printed out a bunch with check boxes before each individual item or task. And if you don't know what i mean by exhaustive, i had "hydrate" at periodic points and "meal break". I even had the very last item "crack a cold one" (as if any of us need that on a list!).
I then evaluated what the customer wanted and simply took one of the checklists and checked off the items i would do based on their work request. For example, lets say i had a customer who only wanted an exterior wash and wax. On my exterior checklist i checked all the items pertinent to only doing what the customer wanted but basically it came down to wheels, wells and tires and then a wash, clay, dry and LSP. Yes, even way back then i could NOT do an LSP without at least claying the paint.
They helped quite a bit because i was one of those people that always did MORE than what the customer wanted. My system corrected that and the good thing to find out was how blown away most of my customers were when i ONLY did what they wanted and expected.
I will say i don't use them anymore as all of my tasks to complete have become rote however it helped me immensely to insure i didn't jump around or get ahead of my actions insuring everything was done right. I remember moving some sequential things around but you can tweak all you want to find what works best for you. Just don't forget to check the list either while you're working or certainly before the customer arrives for pickup.
I also had lists of my supply inventory. Again, made it easy to go through my materials and simply put a check next to something needing to be reordered!
I've always been a "list" person. I can't trust my brain's RAM/ROM function enough.