well first off you should view hunting as food for survival so to speak. don't get caught up in all this big rack craze or trophy hunting.
as for an animal suffering. if you shoot them in the heart or lungs they'll suffer very little. and to do this all i can say is practice,practice,and practice.the more you practice ,the more consistant your your shooting will be to make a good shot placement and with that you'll feel more comfortable and confident.
oh and also this is a great place to learn alot!