That is one of the most common things for a new archer. They are either afraid of the string hitting thier face or arm. With proper form and the right fit it shouldn't happen.
When I draw I like the string to lightly touch the tip of my nose and lightly lay against the side of the face (the corner of my mouth). Don't dig into your face or force the string into it. I promise you will not get hurt. You might feel the string slide past your lips or face but it shouldn't hurt you. The only way to over come it is to just do it.
The exception to this is if you have some odd peircings in your nose or lip that the string could catch. This could be very dangerous and if you have them I highly suggest removing them.
Here is pic of how I shoot. It's not perfect form, but it works well for me. The best way to learn is either have someone compitent watch you shoot. Or take pictures of yourself shooting and compare it to pictures of pros. I looked at lots of pictures of pro shooters and just tried to emulate what they did. To be honest you can shoot any way you want to as long as you do it consistantly. But without some solid anchor points it will be hard to be consistant, as you are finding out.
Good luck,
Paul