You can flex your elbow slightly, rather than locking it out. This will give you better recoil control. Ideally, you don't want the gun to torque off to the side when you fire, but rather pop straight up and down. This is difficult to achieve in one-handed fire, however.
When shooting, remember to ease the trigger forward after each shot, so that you feel the trigger reset (it's a fairly distinct "click" on the XD). Don't let the trigger fly completely forward.
Also remember that, for self-defense, you don't need tiny little one-hole groups. Groups you can cover with your hand are adequate for defense, as long as they are centered in the upper chest of the target.