Take a stereo sample and invert either the left or the right. The result is subtle but interesting.
More fun:
Delete one or more of the first wave cycles of either left or right.
If you only do the first part you’re running in to dangerous territory for mono compatibility.
I think you will have to take much care when doing this. It seems to give nice width, but will mess up your sound in very undesireable ways. Mono compat is about more than just playback on mono speaker. You can get similar effect with the stereo expander “surround” slider.
Better layer slightly different versions of the same type of sound, pan the versions to opposite directions. Then you can also try to align transients and/or phase to make it sound more like a single sound. This way you can get mono compat width - when mixed together, the sound will just get slightly muddy/hazey instead of cancelling itself.
Other than that, gaining width from narrow or mono sounds, while keeping slick sound, is more about subtle width gaining steps building up without destroying mono compat and without creating audible artefacts.
Put stereo expander set to mono on the master bus, toggle on/off often, it will also train your ability to critically listen for spatial information without special effort. A good mix must still sound nice (especially the bass) when reduced to mono!
Or a free VST Plugin:
https://www.izotope.com/en/products/master-and-deliver/ozone/ozone-imager.html
