Clean your rocker with a damp cloth to remove any dust or debris.
Remove some of the finish from the top of the arms, along the sides of the rockers and on the seat using a piece of fine-grit sandpaper. Sand with the grain of the chair and don't take off a lot of wood. The idea is to make it look worn, not to damage the chair.
Wipe the dust off the chair with a tack cloth.
File down the ends of the rockers and the arms using a wood file. Go with the grain of the wood and use long strokes to make a curve over the ends.
Knock a few chips off here and there, using a hammer, on the rockers, the edges of the seat and anywhere else you feel would be interesting. Don't break off a lot of wood; you don't want the chair to break.
Simulate wormholes in the wood using an ice pick. Usually these holes are clustered in one particular area.
Scratch the wood with a wire brush in different places.
Splatter black ink on the chair with a toothbrush to simulate flyspecks. Make sure you protect the surrounding area to avoid splattering ink on other furniture or the floor.
Paint over your work and then wipe down the paint coat with a paper towel or rag to allow the distressing to show through.