Make sure that the small, plastic ball has been removed from the pen's tip. When a gel pen is new, it is shipped with a small piece of plastic on the tip to prevent the pen from leaking during shipment.
Move the pen in circular motions on a scrap piece of paper. This facilitates the ink flow to the point of the pen.
Shake the pen briskly. This will help to dislodge any air bubbles which may be preventing proper ink flow to the tip.
Heat the tip of the pen over a kettle or a pot of hot water. This helps to loosen the ink, which can congeal if the room temperature is too low.