Inspect other distressed projects before you attempt your own to get an idea of the level of distressing you want. Look closely at the details and, if possible, ask how a particular type of distressing was done, since different tools leave different marks on the wood surface. Finally, test a section of stained wood -- preferably a scrap piece of wood -- with the various tools to see which tools' marks you prefer.
Scrub the surface with a piece of sandpaper in the direction of the wood grain to create a "scuffed" look. Lighter sandings will leave lighter scuffs. Strike the surface with a hammer to create dents, with varying depths depending on how hard you strike the surface. Use a short piece of heavy chain to create multiple impact marks at the same time. Avoid striking too hard as you are looking for distressed dents, not actual damage to the wood.
Achieve deep cuts with a hand axe or hatchet, or you can strike the surface with your striking board, allowing the nails or screw heads to bite into the wood. In addition, you can experiment with the various tools to create marks of your own preference -- scratching, dragging or otherwise impacting the surface to visibly mar it in some way and create the illusion of damage over time.
Polish the surface of the wood around the distressed marks with a piece of sandpaper or use a buffing machine to smooth out all the rough edges around the distressed wood. This will create the illusion of the distressing having been performed over time, with the edges smoothed over time. If preferred, add a layer of stain afterward, or leave the distressed areas visible as if they have actually occurred over time.