A common technique flaw many lifters have is the barbell drifting away from the body. Not only does this make things harder from a leverage standpoint, it can be injurious to the back as well.
A simple drill I like to use is adding a band. Wrap one end around the barbell and the other around something that won't move – a power rack, or my bicep, for example.
The idea is to resist the pull of the band in order to engage the lats and keep the bar close throughout the duration of the set. If someone doesn't know where his lats are, he will after this drill.