Usually the eyes go blue, and then oddly enough, they clear up just before the shedding takes place. This can actually make it seem like your snake has shed, and the skin has vanished, when in fact they haven't shed yet! The eyes will clear before shedding, but the skin will still look ugly and dull, so you know that he has not shed yet.
I would concentrate on your humidity. When my snakes are about to shed, I mist the cage with hot water as often as needed, to maintain a constant humidity reading of 90%. You may need to cover a screen top in plastic, if you have that kind of top on your cage.
They do need a period of darkness though, which is why you should not leave the daylight bulb on all night. You could supplement the heat at night by adding an undertank heater if you don't have one already. If you do, just measure the temperature on the substrate, above the heater, and that's the really important temp, not necessarily the air temperature.
I know my posts are long! I just hope that they are useful to you.