I've had many new vapors ask what Nic level they should start with. What i tell them is start low or at least something similar to what they are currently getting from their cigs. Ultra lights 6, Light 12, Full flavor 18 and something like a NP 24. If you start low you will notice you vape a lot more. So next time buy a higher level until you find what works best. If you start high, it may make you sick or discourage them from vaping and they give up.
I was a pack, plus a day smoker. Started with 18mg and it seemed to hit the spot. Started mixing in some 12mg vapes a couple of weeks ago and it's going well.