Okay, I'll give this a shot......... a tutorial of sorts I guess.
Use your hand to measure, for most men 6" is about the width of the hand plus the thumb.
When stripping wire to make up a box I give myself 8"-10". Really for the PITA of short wire it's just not worth being stingy.
Here's the demo board I made for this. Rather than ruin a four square deep box I used an extension ring I had laying around.
Since most people at home will be using romex I've added two pictures, not sure if it will show. Using the cutting surface of strippers, linesmen or the like just barely put enough pressure to make a crease.
And pull.....
There should be no creasing of the wires underneath. Often it seems problems arise from using too much pressure in the stripping process. I'll add I've never used romex strippers and don't know if they are useful or not.
For romex there should be a minimum of 1/4" of insulation inside the box.
Mess o' wire in a box.
Wires now grouped and bent at a 90 coming out of the box. Note, in this example I didn't use any white wire as a non-neutral. If your using a white wire for anything that's not a neutral take a sharpie and color it.
I find it helps when twisting wires with pigtails to bend the last inch or so at a 90, and hold the pigtailed wire at a 90 as well with the other leg of the 90 held in your hand.
Additionally you should only strip5/8"+- or so when twisting 5 or less wires. The will assure that no bare conductors have the opportunity to find ground.
This cut in box is now ready for a device.
A good tight twist. Note the twist should stop just past the bare wire, and the length of the bare wire is covered by the wirenut.
All the boxes pigtailed and ready to fold and device.
Wires neatly tucked away. There is no rule as to which way to fold. I generally Z but sometime like with the black wires I'll make an L that lays nicely to the back of the box. I don't like twists or curls as I find the wires start to fight each other with tension as you try and make them flatter to the back of the box.
Devices added. When laying out the wires coming out for a device you can plan ahead and know that the ground and neutral will always be on the same side and or end area of the device with the hot opposite.
Whenever I'm devicing in metal boxes I usually courtesy tape the exposed terminals. You never know when a screwdriver will slip and could short things out.
Part way through the Z fold of the devices.
And devices landed. Not that even the GFCI in the cut in box with 8" of wire had plenty of room as to not have to push hard to get it in.
And it can all be easier and quite neat when it's just a J box and with no devices.
This technique is just a general ideal and can be tailored to work well with, or help, making up any box.