Depending on your arm length, a good place to start is on the descent, the bar should touch the bottom of the sternum. The idea is for the elbow and wrist to be straight up and down( wrist not forward or behind the elbow). You don't want your elbows out, you want your arms to to
follow down the side of your ribs so-to-speak. Keep your arms closer to your body rather than flaring out to the sides. (This will cause injury over time)
Also, do the reps for a partial range of motion - from the chest to half way up. Don't go to full lockout on each rep.
If you don't feel the pecs after this......I don't know what else to tell you.