Scribble on scrap paper
Warm the pen tip in your hand
Dip the tip in warm water
Wipe the tip clean
Shake the pen gently
Press the tip down on paper repeatedly
Retract and extend the tip if it is a click pen
Twist the barrel if it is a twist pen
Replace the ink refill
Replace the battery if it is an electronic pen
Store the pen tip-down for a short time
Use rubbing alcohol on the tip
Roll the tip on rough paper
Open the pen and check for dried ink
Clean the tip with a cotton swab
Try a different paper surface