Lie flat on a weight bench with a 5-6 kg weight in each hand.
Raise the arms until they are straight up and bend them at the elbow until they are level with your ears, and then raise them back to the starting position.
Breathe in on the downward movement, and out on the upward movement.
Do as many as you can, rest for 1-2 minutes and repeat.
Be careful not to hit yourself in the head.
If you're not able to get to a gym or work with weights (I don't know if you're male or female)...anyway, an easy exercise for triceps you can do at home (or the office, if you have a private one) is to sit in a standard chair that has arms. Scoot forward so that your bum is level with, but not sitting on, the seat. Bracing your hands on the arms of the chair, slowly lower your bum until it's near the floor, then raise back up.