Not knowing yourself, and factoring it into the equation as best you can balanced as best as you can with the experiences of others, is the top mistake IMHO. Its hard to fill a void without considering the size and nature of that void. When you're going to tires plus (or whatever tire store) and you walk in, and just buy any old tire, theres a chance, a very large chance, that the tire you choose isn't going to fill the void its meant to fill. It might be too big, or too small. Know your needs. Were you a light smoker, or a heavy smoker? Did you inhale deeply or lightly? That was my worst mistake three weeks ago - underestimating my own needs, because I never bothered to or even thought about identifying them. I underestimated mine, greatly.
Second, not having enough information with which to to best decide how to most accurately and efficiently fill the void you're about to create when you drop the analogues. I did that. Ended up spending twice and three times, to get a device that delivered in a way that met my needs - both because I didn't identify them, and because even if I had, I didn't know enough about the devices themselves and their accessories etc, to get close the first time.
Save yourself from that - READ this forum as much as you can.
Third - not enough supplies. We as smokers are fairly accustomed to buying a few packs or a carton, and resupplying before we run out. Thats what we did as smokers. Its not as easy or simple for alot of those switching to vaping. For those in an urban area it may not be so bad, but its 4-5 hours for me to drive to the nearest vape shop in person lol. Do what you have to to fit it into your own situation. When you find an e-juice that you like and can vape all day, keep it on hand and order before you need to if at all possible. Same goes for carts and/or clearomizers. Better to have it and not need it than need it and not have it. The unpleasant alternatives can range from vaping a juice you can't stand, to breaking down and going analogue because you're out of carts/batteries/juice.
Hardware wise, as others have said - backups for backups for backups - and bounce that off your own intentions. Meaning: is vaping a vehicle for quitting, or is it a much safer alternative to smoking, for you?
Know yourself, know your situation, know your intentions, read read read and try to do the best you can to make vaping fit your own personal void in a sustatainable way that can keep you off analogues for as long as you need it to.
