Today, another small but important tip:
When you shoot portraits, stick some painter’s marking tape onto the floor exactly where you want to subject to stand.
Why? Well, if you shoot with manually set flash, you will want to keep the subject in the same place, because if they move even a little closer to, or away from, your lights, you need to re-meter and re-set your exposure or your flash power. But even when you use TTL, there is a lot to be said for consistency. Your light direction is paramount, and small changes in position can dramatically change that. Finally, the marked spot makes the shoot faster: no need to subjects to constantly be told where to stand.
So make life easy for yourself: “X marks the spot”. This way you can make every shot consistent and successful.