basically if you're just asking how to make the pictures look more like they do to your eye, what you can do is take a picture, review it, and adjust accordingly (using exposure compensation or going into manual mode) to make it brighter or darker. keep in mind our eyes constantly change "exposure" to match the situations. cameras don't. you can also try a different ways of exposure metering (spot/center weighted/matrix/etc.) to see which works best for that first reference shot.
if you're asking how to do series of comparable beamshots like the ones in my link, you will definitely need a camera which allows manual settings if you plan to take series of beamshots which can be compared amongst themselves. for this basicaly just look at the lights you will include in your series and also potential future lights, and choose a light which is around the middle or above average brightness in the range as your 'standard'.
first, if your camera allows you to set focus manually, focus manually on the target with good light (with the lights on or in daylight). go into your camera settings and make sure your camera is set to a fixed ISO (i.e. not auto-ISO). then set your camera in P or auto mode, and take a picture or do a half-press on the beam of that light. i prefer to use center metering. note the shutter speed and aperture, and use this as your reference. go into manual mode, and then dial in that shutter & aperture, set the camera to a standard white balance as well, such as daylight white balance. once you've locked focus, ISO, exposure, and white balance, you're pretty much all set to go. just note these settings down and you can pretty much go back at any time to take more beamshots with the same settings (although you probably will need to set the focus each time you go back). for long exposures, you probably want to use a tripod and the timer/remote feature on your camera to avoid camera shake.
