I used this guide to successfully replace the glass on a 2012 unibody 13” Macbook Pro.

If you are replacing the glass due to cracking/breaking, you’ll want to cover the entire surface with clear packing tape to keep shards from going everywhere. You can’t use the suction cups, since the glass will continue to crack as you pull on it, breaking the suction. I used an iSesamo and heat gun to pry the edge up, and then scrape off remaining shards around the edges.