Tone Deaf is right on.
--Be able to pull the recorder out of your pocket, in total darkness, unlock it, start the recording, and lock it.
--Be able to connect mikes to preamps and preamps to the recorder, again in the dark.
--Be able to rig up in about 2 minutes in a bathroom stall with a minimum of equipment and gear bag.
--Being able to judge the volume based on your ears, and get the settings right for your rig. This will take 10-15 shows. Do it at home in front of the stereo if you have understanding neighbors.
--Being able to shut off the recorder and restart it between sets so that the file splits right. Again in the dark.
Bear in mind that many times concert ushers may be standing right on top of you, so you have to be able to do all this with the recorder in your lap, you staring straight ahead, and the recorder covered up with a newspaper, magazine, or coat.