The best tip i could give is to invest in a baby toothbrush especially for your lips. Before you go to bed, after brushing your teeth, wet the toothbrush with warm water and gently brush over your top lip in circular motions. Then rinse the tooth brush under warm water and do the same with your bottom lip.
Once your done, it'll only take a couple of minutes, apply a thin layer of vaseline on your lips to moisturize, then literally once it's sunk in apply a very thick gooey layer over your lips [make sure you're not going to see anyone before you go to bed haha]
When you wake up in the morning your lips will be feeling soo soft and chap free!
After this, then every now and again you only have to lightly brush your lips and add less vaseline at night to keep them that way!