This is sometimes the case straight after filling your clearomizer. To avoid this happening, let the clearomizer stand for a couple of minutes, or swill the e-liquid around the clearomizer to make sure it is absorbed by the wick before using.
Another way to do this is to 'prime' the clearomizer by taking a few drags without holding the battery button. The suction created will force the e-liquid into the coil’s wicking area and will allow the wick to become saturated with e-liquid. Take around five drags without activating the battery, but do not exceed that amount. If you take more than five drags, you may flood your coil and you risk sucking e-liquid into your mouth.