Grab them by the scruff of the neck, if they try and flip around and bite the hemostats, you are gripping too hard. Usually you only have to lock them on the first lock unless your hemostats are old. Always pre-scent, do not move the snake into a different container than the one it lives in (moving causes stress) and when you go to feed the snake keep the rodent at a good distance, at least to get the snake in striking mode and then move a bit closer, but 4" should be the closest you go.

The heat pits on the snake adapt to the changes in temperature, if you put the prey up too close then it takes up all of the snake's "vision", it will adapt and see that as the standard temperature of the environment, essentially turning a neutral "colour" (the same as it almost always sees), thus the snake does not "see" the prey anymore but sees it's environment. If you have it at a distance then the rodent will register as something obviously different from the background (aka if the rodent takes up less than 50% of the snake's field of "vision" then it will not adapt to that temperature and will distinctly see the prey item as something different from the background (not to mention it will be able to pick up a general outline of the object it will strike at, mentally cuing that image as "food").

When you do that the snake will usually, even if no prescenting has been done, start to flicker it's tongue to sense what that object is. It will then have 3 things telling it that there is food: "Sight", shape, and smell. Making it more likely to strike.

http://en.wikipedia.org/wiki/Infrared_sensing_in_snakes

The pit organ will adapt to a repeated stimulus; if an adapted stimulus is removed, there will be a fluctuation in the opposite direction. For example, if a warm object is placed in front of the snake, the organ will increase in firing rate at first, but after a while will adapt to the warm object and the firing rate of the nerves in the pit organ will return to normal. If that warm object is then removed, the pit organ will now register the space that it used to occupy as being colder, and as such the firing rate will be depressed until it adapts to the removal of the object. The latency period of adaptation is approximately 50-150 msec.[9]