Better way to fit wires in electrical boxes?
You can ever so gently stuff them in, but there really isn't all too much that you can do - about the same with any wiring.

The 'technique' that I learned is to push one side in first, getting the majority of it in there, and then roll the device onto/into the box to push the rest in.

Just tighten the screws good enough and you'll have no problems.