Here are the pitfalls I see most often with beginners:

• Overfilling the pod. This is the #1 cause of leaks. Leave a small air bubble at the top.
• Using the wrong charger. High-wattage chargers can fry your battery. Stick with the one that came with your device or a 1A adapter.
• Not priming the coil. This leads to dry hits and a burnt taste that lingers even after the coil is saturated.
• Ignoring low battery warnings. Letting the battery die completely can shorten its lifespan.
• Using high-VG e-liquid in a small pod. Thick liquids don't wick well in pods designed for thinner, higher-PG liquids. Check the manual for the recommended VG/PG ratio.