Check the battery for charge.
Check to make sure the top of the battery is pushed all the way up (away from the spring) Rotate the battery in the case.
Check the that the white connectors are fully snapped together.
Make sure the cartomizer is completely screwed on to the gold 510 connector. If it has unscrewed at all, your connection will be lost.
Fully depress the button, some buttons need more pressure than others. It's slight but can be the problem.
Your mod should not gurgle. (like sucking the last bit of soda out of your cup through a straw) It can pop and crackle but not gurgle.
Unscrew the tank from the 510 gold connector. If there is juice in the connector, wipe it out and dab the end of the cartomizer gently until no juice leaks out. You can even turn the tank and cartomizer upside down for a minute or two. Cartomizers are tempramental to say the least.
Make sure that the bottom of the cartomizer is flush with the bottom of the tank, there is a groove it fits into. If it is not flush, it will leak.
When initially filling your tank, insert the cartomizer, fill the tank with juice. Replace the cap, then, with a brand new cartomizer, drip 12-15 drops of juice into the cartomizer, right into the center where the white fiberfill is. If there is not enough juice in the cartomizer it will burn it as soon as you hit the button.
Hard to Draw
If you are having trouble drawing and you are having to suck a lot harder than normal, it's time to change the cartomizer. They seem to get gunked up after time. Near the end of vaping a 6mil tank of juice, it seems to get a lot thicker also. I like to dump the "dragon spit" and wash out the tank. I have tried just adding more juice, but it is never as good as a fresh tank of juice with a fresh cartomizer and fully charged battery.