a much easier way to train the 'archery' skill in by throwing, because that trains both skills ad the same level, so find a tile with something you can pick up (black sand, rocks, clay) or just throw something of yours on the ground (remember to pick it up when you are finished). so, press [g]et, used abcde to pick the item, [t]hrow, use a-z to pick the item, enter to throw it on the ground under you so you can pick it up again. congrats! you threw something, you should now have 30 exp in throwing and archery (if you didnt put points into them at the beginning) you will have to do this 600 times to gain the 18000 exp necessary to get legendary thrower/archer, so i recommend setting up a macro: on your tile, press ctrl+r to start recording a macro, perform the throwing procedure once (or twice, or 3 times (or 7 times to be most efficient)) and press ctrl+r again to stop recording. if you press ctrl+p, your character should carry out the action and throw *sand* onto the floor. then press ctrl+u to set a custom macro playback, 99 to play the macro 99 times, and ctrl+p to execute that, and after a while, (you can afk this bit) youll have legendary thrower and archer before youve even left your village
BEWARE: the only way to stop a macro playing is to move your mouse off the DF window or open another window, this means you cant watch youtube while the macro is playing, and you may get attacked and die if you cant stop the macro, human_dictionary and the bay 12 games forum inc. take no responsibility for damage caused to adventurers and morale while using macros™
(if you do stop a macro, the 'playing' text will flash at the top, just find a safe spot and play the macro again a couple of times using ctrl+p and it should go away)
P.S. save the macro you are currently using with ctrl+s, and load macros with ctrl+l