You want to flex the triceps before you ever start the first rep. This will force you to stop doing that stupid and ugly biceps curl where the biceps actually never get fully lengthened.
As you flex the triceps, pack your shoulders into your back pockets. This is a really low- rent way of telling you to retract and depress the scapula. What this does is keep you from getting all Hulk'd up at the initial start of the concentric. You know what I'm talking about – where you flex the traps and turn the barbell curl into sort of a reverse-grip clean.
On every rep, the focus should actually be on the eccentric/lowering phase. If your biceps growth has been non-existent, then accentuating the negative phase of the curl should cure your puny biceps woes. Take a full 5 seconds to lower the bar on every single rep.
We're now going to take a page out of Arnie's book and actually include some "cheat curls" to extend the set. You use just enough momentum to get the weight past the sticking point to grind out a few extra reps.
The Formula: Sets and Reps
So that's 4 sets of 5 reps with 3 cheat reps at the end to extend the set. Let me repeat this. You need to be able to perform 4 sets of 5 reps with a weight you can use with strict form, taking 5 seconds to lower. Then you use a slight amount of cheating to eke out reps 6, 7, and 8, where you continue to lower those reps over the course of 5 seconds. Take 2-3 minutes of rest between sets.