Breath

There is nothing more important than learning how to control your breathing when performing a threshold interval.  You can (like I did today) kill you power screw up your form by not relaxing and breathing.  Practice focusing on your breath while you are making hard efforts in training so you don't wear yourself out in a race--or hard group ride. 

While focusing on breath, also make sure you are smooth on the bike and not wasting energy.  Form is so critical to maximizing your energy/breath/power.