In the beginning when the g.b. is new and tight, reverse can be a little difficult to slip into. I found (in the beginning) it was easier to grasp the lever with my hand (palm on lever knob) and using a "stiff arm", pop the lever back using a little body weight. You can "feel" what is going on better than if you are using your boot.
There is actually two detents/notches to the neutral/reverse lever; the first will get you into neutral, the second into reverse. If you are aiming for neutral it really does not matter which you get into...just remember to move the neutral/reverse lever fully forward to stay in neutral. Some g.b.'s if the lever is just slightly aft a hair...you can not engage any gear. Usually happens at a traffic light and you'll think your g.b. just went out.
Later, after you get the feel for it, and the g.b. loosens up a bit...you can easily use your right heel on the lever to bump it into neutral or reverse. Once the g.b. is well worn (10,000 Km's or so) it will just about drop into reverse with little effort.
The adjustment for the neutral lamp is the nut/screw/wire just ahead of the lever in your picture above. Loosen the outer lock-nut while holding the screw steady with a screwdriver. Back the screw out 1/2 a turn or slightly more. Turn the ignition "ON", put the g.b. in neutral and slowly (very slowly) turn the screw in (CW) until the lamp illuminates. Slowly depress the shift pedal to see if the lamp flickers...you should continue adjust the screw until the lamp does not flicker or go out until you are starting to feel pressure (or slightly before) on the shift pedal BEFORE going into 1st gear. When happy, tighten lock-nut whilst holding screw steady. Does not need to be gorilla tight, just snug. BE CAREFUL AS IF YOU SCREW THE ADJUSTMENT SCREW IN TOO FAR IT WILL NOT ALLOW YOU TO SHIFT THE G.B. AND CAN SHEAR THE ADJUSTMENT SCREW OFF. You have been warned. It is not as scary as it sounds.
If you are curious as to how all the bits and pieces work together in the g.b.....go here:
http://myural.com/how_the_gearbox_works.htm