An under-powered battery may not be able to vaporize the e-liquid sufficiently, leading to excess e-liquid leaking out of the atomizing chamber. Also make sure your battery is under 90 days old, as all batteries wear out after continued use.
It may sound like a silly point to make but not every pod kit is made to operate the same. Vaping on a pod kit incorrectly can cause problems. For example pod kits like the STLTH are designed to be vaped mouth-to-lung (like a cigarette), whereas a kit such as the SMOK Nord can be used both mouth-to-lung or direct-to-lung depending on the pod that's installed. Be sure to check that your vaping method is right.
Taking big, deep drags on a pod mod may lead to too much e-liquid going through the coil which cannot be vaporized properly. This usually proceeds to then leak out of the mouth piece. Try taking gentle drags to ensure the e-liquid is sufficiently vaporized.
If a vacuum isn't created in your mouth when vaping on a pod (like when sucking a straw), the excess air may encourage more e-liquid to be drawn into the coil that will then leak out of the mouth piece.
Every device has a way of in-taking air, as this is what fuels the vaporizing process. In most pod systems, these will be small holes on the side of the device itself. When you're vaping make sure your fingers aren't over these in-take holes; this can cause the suction to pull e-liquid through instead of air!
Blockages in the centre pipe will restrict the airflow and un-vaporized e-liquid will eventually make its way out either through the mouthpiece or through the airflow holes. Also ensure that the pod has been inserted into the device correctly according to the manufacturers' instructions.