Hi there,
From a postural perspective before you even start the movement, you need to engage your lats first. Then as you begine your movement, imagine you are trying to squeeze a five dollar note in between your shoulder blades. You should always remember not to fully extend (straighten your arms) too. I had problems with getting my shoulder stabilisers to work and had signs of winging on my injured shoulder. From a personal trainers perspective, I totally agree with the above post. I'd also add that before you start the exercise always remember to switch on your tummy first, then engage (like your lats are being drawn downwards) before starting the exercise. I'd start with a seated row and gradually move onto other variations.