first, take out the cartridge, with a paper clip (through the little hole in the mouth piece). Wipe out all the excess
juice and if possible, wash off the nic
juice from the mouthpiece.
Now, re-insert the cartridge, and draw nice and slow. Quick draw/pumping only pulls the
juice. Once you learn the drawing for your model, it shouldn't be an issue.
See, it's like a straw - that when you draw, the nic juice from the cartridge gets "pulled" to the atomizer wick - and evaporates... then the vapor follows the little side hole of your inner cartridge. (The cartridge isn't fully round - you see - to allow air movement). If you draw too hard and too quick, the juice won't have time to evaporate and just get pulled to the air-way and get in your mouth.
Nice and slow is the key.

Also, a quick.. like 1/4 second light puff before really drawing to prime your atomizer (makes it nice and warm, so that it will evaporate the juice effectively) is a good solution too.