Hi, Sabrina. Assuming that your floor does have a varnish finish, first wash with Tri-Sodium Phosphate (TSP) and rinse well. Then lightly sand the floor to break down any gloss and give the surface some "tooth". Use 150 grit paper with a sanding block or an electric finish sander and, again, sand thoroughly but lightly. Then vacuum the dust up and then go over the floor with a tack cloth to get ALL the dust up. You should now be ready to prime and paint.