This guide contains a few examples to conceal your Zis-3 using camouflage nets. Camouflage nets do not substitute tactics and placement, and good placement (with lots of natural foliage and clever position) will always outdo these examples. These simply serve to be lightweight alternatives to using the net canopy.
I might update this later if new ideas come up. Generally, this guide should server as a guide for your own creativity. For me to give you every single possible arrangement is silly, so mix and match as you see fit.

Cost: 100 build, 25 ammo
The best possible arrangement for hiding your gun in a forward-facing scenario. Offers nearly perfect concealment and vision. This is map-specific. For example, in this example, the sandbags in front are what let you cover the barrel perfectly. Fails at slight angles away from neutral position. Therefore, this is not always possible or ideal.

Cost: 150 build
Alternative that works in most situations. Reduces vision but hides barrel and front completely. Also allows higher range of motion.



Cost: 50 build, 25 ammo
A decent choice if you're more concerned with visibility from the sides. The high barrel cover is decent for valleys and positions with existing short concealment. You could add an inf. cover or a lean-to to hide the lower sections. The cost of hiding the barrel is reduced vision.



Cost: 50 build
The cheapest option for good all-around concealment. Muzzle will always poke out, however. Vision is reduced.

Even though concealment is essential, without being able to see or hit your target, it's useless. Always make sure you aren't sacrificing too much vision for concealment. Additionally, try using muderhole fortifications to break up your silhouette/color.
Do not try to angle your lean-tos or put them too far forward. You will blind the gunner. Always test in training before doing anything.