First of all, you will need to remove the door from your home.
Then place it horizontally on wooden trestles, if the door has glazed openings, masked with ribbon and close with paper to prevent the glass from getting dirty or scratching.
Look carefully at the surface of the door, if there are holes or dents, roughen the area with sandpaper and then grouted in order to level the surface.
Now we prepare the primer for painting, roughening the surface with abrasive paper, the door is then dusted and degreased with paper and alcohol.
The whole door must have an opaque and smooth look, only this way the new paint can adhere well.
If it had already been painted, insist with the paper to reduce the thickness of the paint on the edges so that the door does not rub against the edge once it has been reassembled.
Repeat the operations after drying the paint very well on the other side of the door.
Chemical sanding or stripping
The sander is useful for removing the paint and making it opaque to repaint but you will need to insist a lot to remove all the thickness.
In case you want to remove all the thickness it is advisable to apply the chemical paint stripper in gel with the brush and then remove the wrinkled paint with a metal spatula.