You can "dip" arrowheads into an Oil barrel, and make Slowdown arrows for your ranger, which are as priceless in combat as they are extremely cheap to make. It's also possible to get Stun and Knockdown arrows cheaply, but not in the same amounts as Slowdowns.
Another good tip is to always send the ranger to the flank, away from the main group. And do sneak-shots from there. Sneak, shoot for double damage (Guerilla), sneak again at the end of the turn, then do a sneak-shot and a normal shot the next turn.
