What can i do to avoid lip biting?

Bite check: If it's a habit then you have to break the habit. If it is happening unintentionally then you need to get your occlusion (bite) checked and possibly adjusted.

Know why.: To avoid it, you need to know the cause. Most lip biting is related to a [bad] habit or the way you bite (occlusion). The first one has the simplest (and sometimes the hardest) solution: stop doing it. The second involves balancing and aligning your bite to keep you teeth from pinching: the solution could be orthodontics, crowns, new dentures (if you use these), or other treatment. Ask your dds.

Straw: Try biting on a straw instead of your lip-chewing sugarless gum with xylitol may help.