First a quick cleaning, if there is anything stuck to the surface use a razor blade or putty knife to gently pry it away.
Then, wipe down the piece with a slightly damp cloth to remove any surface dirt.
Make sure when you're sanding to work in good light, it will illuminate the imperfections.
To remove a previously stained finish, start with a medium grit paper. i'm using a 60 grit to start this project. I have a random orbit palm sander that i love because it ensures an even finish and quickly works through the grits from coarse to fine.
To get into angles and crevices. Fold a standard sheet of sandpaper and use the point of the fold to remove material from those tight spots. The edge of a sanding sponge will also easily reach those tight corners.
After each round of sanding use a tack cloth to remove dust from the surface. A small vacuum or a paintbrush can help to get dust from crevices.
Continue sanding working up in coarseness until you've reached a super fine grit for a super smooth finish. I'm Mrs. Fixit and it's just that simple!