Strength adds to damage for both melee and non-gun missle weapons, though not quite as much to missle weapons. (100 str = +100% dmg melee, +50% damage missle). It also adds stamina and carry capacity, which are both very handy for a Ranger.Your base arrows only do 3-7 damage and your base quarrels only do 5-11 damage, so you won't be shooting for a whole lot of damage until you start getting better ammo. Many bows also add a damage percent bonus which will help get more out of your ammo. Don't forget that your Ranger will also occasionally get critical hits with any ranged weapon, based on their Ranged Combat skill.
Speed and Dex both will help improve your rate of fire (and also number of melee attacks). Higher initiative weapons will also in many cases get you extra attacks. (For example, if you're only getting one attack with a -3 initiative crossbow, you might get two with a +4 initiative bow.) Also, there are a few missle weapons out there that automatically add extra attacks, which is quite nice as long as you can handle the stamina cost of those attacks. Since this is the spoiler forum:
Doubleshot Crossbow (+1 shot, Gadgeteer merges two Light Crossbows)
Tripleshot Crossbow (+2 shots, Gadgeteer merges Light Crossbow and Doubleshot Crossbow)
Doubleshot Sling (+1 shot, found/bought in various places)
Senses is generally considered the single most important Ranger attribute, adding to accuracy, initiative, chance to improve the Ranged Combat skill, and granting access to the expert skill Eagle Eye which further improves missle accuracy.
Hobbits are the best Rangers, and Felpurrs and Mooks are close behind. Humans make very good Rangers also. If you want more Vitality on your Ranger, then Lizardmen and Dracons also become good, but they are still behind Hobbits overall.