I smoked the better part of two packs for over 40 years, and had no idea of what strength nicotine to buy at the vape shop when I started. The little gal there was very sweet, but probably didn't really know what she was doing, lol. But I didn't either, so I took her recommendation and started with 12 mg. It kept me from smoking for several days, and I didn't really have what I would call a craving, but just that vague, anxious, something's missing feeling.
I went back and got some 18 mg which worked so much better in a matter of a few hours. So keep in mind you might have to experiment with different strengths to find what works for you.