To understand width you must first understand the opposite of wide – mono.
Mono is the ultimate narrow. Mono or rather a sound “panned center” just means the exact same signal is coming from the left and right channels. Thus it follows, the more different the left and right sides are, the wider things will sound.
If you take a sound and delay one side by 30 milliseconds, it immediately sounds wider. It’s just how we perceive things. If you use one mono sound on the left and another mono sound on the right, say a buzzy synth and a clean guitar, it will sound very wide.
The more you can make the left and right different, in phase, tonality, timing, rhythm, dynamics, harmonic content, the wider they will sound.
Aside from that, MS processing is always a great way to go, just be smart about it. Like anything, Too much and it sounds terrible.
For dance, pop, or EDM, you don’t need much below 100 or 200hz on the sides. I’d probably say 150-200hz. For rock/alt/country/indie/folk/ja
Try to avoid “Big Mono”. Look it up. It’s a thing. Drop a side and pan it, or delay a side. Big mono is not wide. It kills width.
Be very choosy about what goes up the middle. Only the best stuff can go up the middle, in ANY genre. You should be able to solo the Center panned elements and it should sound GREAT with those things. No masking. No weirdness. Solid height from low to high frequencies… if you’re not familiar with that analogy, look it up! (Height in regards to frequency) Then worry about the stereo stuff.
I’m also a fan of LCR panning with the VERY OCCASIONAL 50/50 spot. Like maybe 2 or 3 things in a 60 track mix. Usually it’s just the toms or something very sparse.