After the edges have been cut in, roll the ceiling using 9 inch roller and an extension poll. Take about 2 foot wide section across. Over-lap your cut in strip as you go. When you reach the side wall, start  rolling another 2 foot wide section overlapping the first by a couple of inches. Continue this process until the ceiling is completed.

 
Roll the walls. Start in a corner at the top. Roll a 2 foot wide section from top to bottom overlapping the cut in strips. Roll another 2 foot wide strip from top to bottom overlapping the first by a couple of inches. Continue this process until the wall is completed. Move on to the next wall working your way around the room

When rolling a wall or the ceiling try to finish the entire wall or ceiling before taking a break unless the wall or ceiling is divided into sections. Then you may take a break between sections. This is most important when working with the finish paint.
Trim Now use a suitable wood primer for the trim.

An oil/alkyd base interior wood primer will also make a good first coat over the factory painted heater. Paint only the outside of any heater. Do not get any paint on elements. Check manufacturer painting recommendations before painting a heater. Use caution especially with electric heat. See Safety