The effect of this constant tension is a longer contraction time on the muscle, which basically makes the exercise a whole lot harder.
With this in mind, you should make sure you start with a slightly lower weight than a normal barbell or dumbbell curl.
As with all bicep exercises, your main points to think about are squeezing the heck out of the bar and attempting to supinate the hand.
I say attempt, as you will not actually be able to do this, but you can press your pinky finger into the bar like you are trying to twist your hand.
As it is a standing exercise, you should also make sure you have an upright posture, a wide athletic stance and you are holding the bar/handle with a shoulder width grip.
Take a look at our video tutorial below to see the fine form points of this exercise, and if you need something to print off and take to the gym, you can find our step-by-step exercise technique further down this page.