If anyone wants to enter the world of Advanced Personal Vaporizers (APVs), look no further than the eGo-C Twist/Vision Spinner and a well known/much reviewed Rebuildable Atomizer (rba) like the Vision Eternity.
I think a lot of people will disagree with this one. Sometimes one wants to crank the voltage higher than 5 V, and have 3000 mAh of power to get through the entire day, along with some of the other capabilities offered by the 18650 mods and such.
My tip, a very common tip that I'm surprised has not been mentioned yet:
Have backups for your backups and then have a plan B for the failure of all your backups.