The French press is a great way to isolate the triceps and get a good stretch at the bottom position.
Begin by holding a barbell at mid thigh level with a shoulder width grip and your palms facing away from your body. Next, curl the weight up to your chest and then press the weight overhead; this is your starting position. Now, begin the movement by bending your elbows and lowering the weight down behind your head. Continue to lower the weight until you feel a stretch in the back of your arms. Next, squeeze your triceps and push the weight back up to the starting position. Lock out your arms overhead and then repeat until you have completed your set.
Start with a light weight on this exercise and master the form before progressing in the weight.
Keep a strong wrist during this exercise; this movement can put a lot of stress on the wrists. Also, make sure to keep your elbows tight to your head and do not allow them to flare out to the sides.