Stretching your labret, is similar to stretching your ears, but it takes a little bit longer, and it pinches a little bit more, due to the lip being a bit thicker, and in constant use.
Beginning, you can do this similar to your ears, you can star with just a basic piercing, dermal punch, or pierce and stretch. If you get it pierced at 1.6mm, it's a little bit more difficult to start, but it's still do-able. I myself, personally got it pierced at 4mm, and stretched straight to 6. It cut out all the difficult small sizes, and started me off with a hole :).
So, you get it pierced at 1.6 (14g), you've waited upwards of 4 months for it to fully heal, and you want to go to 2mm (12g). I used septum bullets, when I stretched my snakebites.
These little items, go up to 8mm, and are perfect for stretching labrets. I myself dead stretched, because it was easier, if not a little bit more expensive as I got to the bigger sizes. Dead stretching is a method of where you size up when you feel the current jewellery is loose. You will need custom jewellery when you stretch your labret, as you need stuff with a flat back so it doesn't rub against your teeth.