Haha...that's probably the trickiest part. I just do my best not to agitate the snakes too much before I shoot. Usually I bring their tubs right outside with me so that I don't have to do more than just pick the snake up and set it on the back ground. If you handle them before had or on the way to photograph them, they tend to get curious or anxious and once they start crawling around, it will be a long time before they settle down.
For more active animals like colubrids, sometimes placing a small container upside down over the animal will give it a chance to calm down a bit and then you can lift the container and shoot while they are (hopefully) a bit settled down.
Some animals will always be frustrating but for the most part, our BPs are pretty cooperative!
Good luck!
Aaron