The transition can be very hard, but the best thing to do when you have the cravings is to vape until the cravings pass, even if you need to vape for 20 minutes. You'll be surprised to see how vaping can really satisfy the craving! If the cravings are really really strong, I would recommend using higher nicotine juice, like 24mg. That will also help kick the cravings.
Good Luck!
One other thing, cigarette cravings are not only from nicotine, but are also psychological. You need to convince yourself that vaping IS smoking! Don't think of it as a "replacement" or an "alternative," just think of it as a different brand of cigarettes! Try to vape in the same routine as you would smoke. In other words, vape when your used to smoking. Think of it this way, your trying to trick your psychological/nicotine cravings into thinking that nothing has changed from the transition from cigarettes to e-cigs.
Hope this helps!