The DP and the Gaffer
A lot of times a DP and the Gaffer are the bestest of friends on set. I often feel that a production can be efficient or not efficient because of this relationship directly. I feel like having a regular gaffer that knows your style and can predict your shooting methods drastically speeds things up on set.
Here is a great series of little videos starring some great UK and American DP's and Gaffers explaining several aspects of the relationship on set and how they work together.