My method, others may vary.
1) Paint a black band around the waterline.
2) When dry mask the black boot topping. I use 3M vinyl auto striping tape since it is flexible and conforms to the compound curves. Paint the lower hull red
3) When dry mask the lower hull. Do not remove the boot topping masking.
4) Paint the deck.
Somewhere along here I may freeplay. On some applications I will paint the deck first, spraying vertically down onto the deck. I then spray the hull color up from 30 to 45 degrees below the deck level. The deck edge masks the overspray from getting on the deck. Finish by hand painting the lower 1/3 of the bulkhead.
On other applications I will spray the deck then mask around all the fittings with hundreds of little snippets of tape. Then spray the upper hull and superstructure.
Lastly, remove all the masking and hand touch up.