CamelBak packs are designed so you can easily adjust them to fit your own body type. Everyone has their own preferences, but here are some guidelines for figuring out where the pack should sit on your body:
If your pack has a waist belt attached, try to set the shoulder straps so the waist belt lines up with the top of your hips.
This will transfer some of the load from your hips to your waist, which means more stability and a better range of motion.
If your pack has sternum straps, slide them up or town so the strap sits just above your abdomen. This will also help distribute weight more evenly across your body.