If the liquid is leaking from the mouthpiece, please first make sure the air pipe was not filled e-liquid. Then verify if the sealing O-rings on the atomizer tube and atomizer head are both intact and in good condition.

If the liquid is leaking from the atomizer base, please check if the sealing o-rings on the atomizer base is intact and in good condition and make sure the liquid level is between 10-90pct. You must also make sure all parts of the atomizer are tightly assembled.

Other leaking problem, you can read this post