At the very least, lightly scuff with a abrasive i.e. sandpaper, clean with a VERY diluted TSP solution, make sure and wait for dry and apply a oil based primer like Kilz. I paint for a living and this will increase the likelihood of your finished paint adhering. Also, use a high quality self-leveling polyurethane based paint. Sherwin Williams has a great product called Emerald series. That product is designed for painting cabinets/trim/doors etc. The self-leveling helps brush/roller marks to “level” out. Now if you’re equipped to spray then the results will be professional.