When you're starting to light a scene, a little light goes a long way. I always start with a light at less than 100%...usually 66% or less. It's easy to 'overlight' and have flares and shadows criss-crossing all over the place. I also like to just Ctrl_D duplicate a light [at, let's say: 44%] and move it around and fine tune by increasing or decreasing the fall-off. But it's lots of trail and error. Use the Snapshot camera to preview small areas. Be patient.