I use a comb to part my hair in a line from my hairline to crown, then apply a small blob straight from the can to my scalp, do a few blobs enough so that when I rub them in it covers the entire parting line and skin a few cm around it. Let the foam melt a bit first so that you are massaging liquid in and not pure foam. I use 3 lines all the way from hairline to crown, one from the left temple, one from the middle of the hairline, and one from the right temple. I also use 2 parts in between each temple and middle partings, but only apply down to the mid scalp.
Lol that was way too detailed, but it's the only way I can ensure I'm getting minoxidil everywhere with the foam. Problem with this is you use way too much minoxidil, and end up feeling lightheaded etc. I've had to cut back to once per day now since it was doing that, and I was shedding loads. Using liquid on the crown at night instead so that I can get a 1ml dose.