I'm going to assume you are painting a porch floor.
Treat your porch like any other peeling surface. Scrape then sand smooth to remove all peeling paint. There could be a lot of sanding to make it look right. The prep is very important, take the extra time now for the best result later.
Priming isn't necessary if an Alkyd Porch and Deck Paint is used. This will be a two coat process. The first coat needs a little thinning to help with penetration. Allow over night for drying, then apply the second coat without thinning.
My favorite brand is Devoe. Their oil base porch and deck paint tacks up quickly and even dries well in cool weather. Choose a good name brand sold through your local independent paint store.