When a wild animal in the open desert does repose enough trust in you to allow you to interact with it at close range, it is an experience that you will never forget. We talk to all animals, which may or may not be relevant to our successes. The sound of our voice does not seem to disturb them. We try to avoid any sudden movements. Some situations lend themselves to cooperation by animals.
Reptiles are likely to be most approachable when basking.
A contented reptile is usually reluctant to leave. Snakes in particular, when they have found a warm road surface when the air temperature is cooling off in the evening, will tend to hold still for close-up photography. You should be aware, however, that rattlesnakes, like people, tend to be grumpy if someone keeps pestering them while they are trying to sleep. Rattlesnakes should, of course, be approached with caution, but unless stepped on or startled, pose no great danger, as long as they are treated with respect. Animals, like people, are blessed with widely different personalities within species.