6. When did you last change your clearomizer tank?

If you are confident your battery is on and working, and that the clearomizer is clear of blockage and cleanly connected to the battery, then it could simply be that your clearomizer (or the coil within it) needs changing.
Clearomizers last anything from 2-8 weeks but are very much consumable items. After a certain amount of use, the coil will burn out rendering it unusable (ie the e-cigarette will no longer produce any vapour since the coil will be unable to heat the liquid). After this time, you will need to buy a new coil (if your current clearomizer has a replaceable coil option), or a new clearomizer.