1) I wash cold and air dry.
2) I iron the collar flat, unbuttoned, and usually then fold it and iron quickly right at the back of the neck to encourage it to stay fully folded.
3) I used to spend a lot of time with my fingers under the collar points during the day, pulling the collar out and such. After a while I realized that the collar responds better to fixing my personal problem - the collar creeping up in the back. Pulling the back of the collar fully down brings out the roll in the front.
4) I also make sure my tie is not too tight. A very, very well-fitting collar (bordering on too tight) will have a good roll even when the tie is pulled fairly tight, but if you pull the tie very tight on most shirts, the tie creeps up your neck inside the collar, pulling the points taut as it does so. I can take a photo of this tomorrow if anyone isn't sure what I'm talking about. Loosening the tie a bit will allow the collar to sit correctly folded, and the points will be relaxed and roll.
5) Other than initially ironing and re-folding occasionally throughout the day, I set it and forget it.

Definitely unbutton before washing

hmmm ... never paid attention to it, have machine washed them in cool, warm, and hot water, have hand-washed them, have unbuttoned the collars and also left them buttoned, but after they're finished washing I do up the buttons and stick the fingers in and stretch the collar out and shape it, and then air dry them, and that's it ...

I don't even iron them ... the slightly rumpled and wrinkled vibe reminds me of the old days

I'd say it depends on the fabric of the shirt. A collar with unfused lining (Michael Spencer) will roll more nicely than an unlined collar from a flimsy madras (Gitman Vintage). Also agree with Patrick that you should unbutton the clothes before washing, or you risk wearing out the button hole.