If you have ever read the first step on any of my other tutorials, you'll know what this step is.
Even when using chalk paint, prep your piece. This will ensure all your hard work lasts for decades, not just a few years. There's a saying that floats around the refinishing world..."your finish is only as good as your prep" and this is so true when painting a piece!
Clean the piece thoroughly, make any needed repairs, sand out scratches, scuff sand the entire piece with 180-220 grit sandpaper, and finally, wipe down with a damp (water) cloth. If you're painting a dark piece a light color, think mahogany wood being painted white, you'll need to prime first. If bleed through is a concern, use a shellac based primer.