Use 220 sandpaper or block to lightly scuff the surface.
Wipe down with the deglosser with a lint-free rag.
Start taping out areas you do not want the paint to get. Lay down a drop cloth on those areas as well.
Optional: Use white paintable caulk to fill in any gaps in woodwork before priming.
Use a paintbrush first to start to apply a primer in small grooves. Work in sections doing a few spindles at a time.
Use a small foam roller to prime flatter areas of your stair railing and banister. Keep checking for drips. You only need to worry about covering the surface (it may not look too pretty, yet).
Let the primer dry. Some primers will be ready to go in an hour and others will need longer. Make sure primer has fully adhered to your surface. You can scrap your fingernail to see if it is ready.
Repeat steps with brush and roller with a white latex enamel paint. You will need 2 coats.
Allow the paint to dry (overnight would be great). Tape out the top and bottom railings. Consider using Press and Seal to protect that last stair spindle.
Use a paintbrush and roller to paint the top and bottom railing with colored latex paint. Paint at least 2 coats.
Take the tape off and touch up any areas.