Wait for five seconds after the first inhale.
After the first few inhales, monitor your feeling. If you feel nauseated, or dizzy, stop inhaling for a few minutes.
One inhale is enough per minute. Breathe some clean air in the intervals, it will keep your lungs healthy.
If you feel light-headed in the first puff, then e-cigs may not be right for you.
It is highly recommended to use the vape pen without the juice, for the very first time. It will burn off the harmful material, so your lungs will remain safe.