The overseas trend is to do fishless cycling but I think that idea is nuts.
Set up the tank. Add water, filter and heaterstat. If you leave it for 5 days or so it enables you to check the temperature has stabilised and is right for the fish you want to keep. The tank will not start to cycle though with just water in it. After you have checked the temp is stable, add 6 hardy fish. Neons are not hardy. If you are wanting to keep platys then add 6 of them. Wait a week then add another 6 fish. Continue this until you have reached your stocking level. This way will build up the bacteria slowly and surely.