Hi Corn snake
Another thing that you have to remember with macro photography esp with slow shutter speeds is to keep the camera as still as possible. Even the press of the shutter release button, while the camera is on a tripod, can create fuzzy/blurred/out of focus images. That's where good lighting comes in. With proper light on your subject you'll get much clearer pics and your shutter speed will be much faster using the av function. I tend to take the subject outside in a nice natural location and use either early morning or late afternoon light (note mid afternoon light is too bright and you may overexpose the photo).
What I've done in the past with photographing snakes outside is to take a buddy along to help with handling and positioning the snake. Use a dark container to put the snake under and then get on your belly (It's very important to be on their level it makes for great pics). Get yourself comfy and your camera settings right (you can use anything from your camera bag to a nice firm pillow to prop up your camera, try not to shoot straight from your hand because camera shake is a big influence on clear photos) and when you're ready let your friend lift the container. The sudden light will "stun" the snake a little and it will take him a few minutes to get accustom to his surroundings. There will also be a lot of tongue flicking that you can try to catch. You can also make yourself a homemade reflector by covering a beer box bottom in tinfoil which a buddy can handle for you to reflect more light on your subject. As soon as the snake start moving cover him again for about 2-5 minutes to settle.
Use the "rule of thirds" method as smeegle suggested and always try to have the eye of the snake on one of these reference points. Always try and capture some light reflection in the snake's eye. This will make or break you photo. The experts are always looking for this. It make the photo come alive.
Most important is to plan your session properly. What's your subject and what equipment you'll need. As mentioned time of day is important, I prefer early mornings because than the snakes isn't so active and they will take a bit of time to warm up before becoming a hand full. Always be on the lookout for "interferences" in the frame. You might not notice them in the view finder at first but it is very frustrating to see later on your computer that your friend's dirty big toe crept up into the award winning shot. Also be on the lookout for unnatural marks made in the sand or surroundings. I always take a little hand broom with to sweep the area every now and than. The marks made by the snake itself is fine. It's not nice seeing a tekkie footprint next to the snake.
When it comes to camera settings I usually shoot with av mode. I try to use f6-8 the most. With this the subject is nice in focus and the background out of focus. My iso is never more than 400 and I try mostly to use 100-200. I also set the white balance to auto. Just remember when you use av mode the higher your f stop the slower your shutter speed will be and then you have to compensate by pushing your iso higher. With iso the higher the more grainy (noise) the photo will be.
When choosing background or scenery to take your photos don't choose backgrounds that's too busy it will also be distracting to the viewer unless you want to illustrate something like camouflage.
I hope this help you when taking pics. Here is some pics I took
viewtopic.php?f=6&t=26704.
Remember practice makes perfect. We are lucky today with the digital age just to erase the pics we don't like.
Regards
Cronje