Distressing gloss painted furniture to make it look old is almost an art form in itself. There is no right or wrong way to age a piece of furniture because the outcome is purely to the liking of the person doing the distressing. However, there are a few techniques you can use to help you achieve a "period correct" look to your distressing so you don't just look like you have a beat-up piece of furniture.
Take a mental note of the areas on the chair that gets the most wear and tear. If your piece of furniture is a rocking chair for instance, you could focus on the seat, arm rests and the rockers. If it is a coffee table, you could focus on the top and corners. If it is an old dresser, you could focus on the top and around the handles on the drawers. Do not overdo your distressing, as it could make your piece look trashed instead of old.
Sand the gloss off the surface paint with light grit sandpaper or #0000 steel wool. Over time, the lustre of a high-gloss finish wears off. Sand the entire surface of the furniture to remove the shine. Do not sand down to the wood unless you are sanding in an area that would traditionally see that amount of wear -- like the seat of a rocking chair might.
Run coarse sandpaper along the edges of the wood to break away paint chips form the corners. You can even lightly scratch the corners with a wood rasp or file. Add a few dents and dings with a ball-peen hammer or mallet. Try to mimic 80 or so years of loving wear. This is where your artistic license starts. You can remove a lot of paint and create a lot of dings or go light on these cosmetic changes.
Add scratches to the feet or runners with a wire brush. The feet, legs and runners of furniture get banged up over time, and every well used vintage piece shows signs of wear and tear at these locations. This is also another area where you can use your ball-peen hammer to accent the damage.
Apply a small amount of dark paint or dark stain to the exposed wood surface with a rag. Let the paint of stain sit on the wood surface for a few minutes and then wipe it off. This will darken the exposed wood as would happen over time when exposed to oils from the human body touching it.