As an amateaur/enthusiest recordist and sound engineer, a lot of the information I get is from occasional hands on experience. I don’t often get a chance to work with other more experienced recordists and learn from them so blogs like this one are a wealth of information for me. With that being said, here are a few things I’ve learned about room tone mostly through painful experience.

1. Unplug everything that makes noise. Drop your keys in the fridge as a reminder to turn it back on before you leave. This not only saves some noise in the recording but air conditioners and refrigerators have the nasty habit of turning on and off and on again. Turn them off and save yourself the headache. 
2. Just get room tone. It’s hard to pin down the director to give time for 30 seconds of room tone. Make sure the first shot is all set with lights and camera and actors and then get your 30 seconds of room tone first thing. This will help you discover anything that is out of place and will interfere with the sound as well as get the burden of remembering out of the way.
3. Get room tone in the same location. Moving just a little ways around the room can change the room tone or ambience a lot. I learned this when I tried to use traffic ambience that was recorded on the same day as filming but 20 feet to the left. It was surprising just how different they sound. The same can be true for a room. Don’t expect the corners of the room to sound the same as the center. That also means pointing the mic in the same direction if at all possible. 
4. Use your recorders back lit screen as a timer. Set the backlight to 30 or 60 seconds for an easy way to keep track of the time. This will give you freedom to scowl at everyone who thinks they can walk silently through the set without making any noise.

Everyone hates sitting around silently for 30 seconds but the amount of headache it saves later is worth the awkward silence.