Nearly all cartomizer issues are the result of under-filling, over-filling, or not waiting long enough for the juice to soak all the way into the wick.
If you are receiving a burning taste or a dry wick taste, make sure that the cartomizer is fully filled. Add a few more drops to the cartomizer and let it sit for a couple minutes to fully wick. Check the fiberfill. If it looks dry (white and fluffy), add a little more juice. The fiberfill should look wet and saturated, but there should not be juice pooling on the top.
If you are not receiving any vapor or airflow, check to make sure that the battery threads and threads on the cartomizer are clean. Make sure that the tip of the rubber mouthpiece is placed into the center air tube and is not sitting over the fiberfill.