Step 1. You see the lizard, you stop! Very slowly get your camera out and take a picture from where you are standing. Don't move to a better position. Take the picture from where you are.
Step 2. Now slowly move in closer watching for an nervousness on the part of the lizard.
If it appears he is getting ready to dart, stop and take your next picture.
Step 3. Now you can slowly move to a better position and maybe get down to his level and get the really good shot and zip.........
...he's gone. Well at least you have two in shots the camera. Better than nothing.