I usually keep a fairly busy schedule so my range time is usually held to 1 or 2 hour sessions at the most and sometimes less. What I do before going to the range is just as important as what I do at the range because it is what sets me up for either success or failure. I will usually have my game plan put together a couple days in advance of going to the range. I will know what drills I want to do and in what order, how much ammo I need, and any other gear I need. Generally I will write down my drills in a notebook and leave spaces for any extra information that might need to be added like PAR times, etc.
Preparing like this allows me to get the most I possibly can out of my time and resources.