If you're stood there holding a pair wondering whether they're too plain to bother with, buy them. The ones that look like nothing on the hanger are usually the ones you reach for on a Tuesday when nothing else feels right, and that's not a small thing. Jersey shorts don't try to impress anyone, which is exactly the point.
Fit is where people go wrong, mostly because jersey has give and you end up buying your usual size without thinking, then finding they've gone baggy round the thigh by lunchtime because there was no structure there to begin with. Look for a proper waistband, elastic with a bit of body to it, not a flimsy strip that rolls over by the time you've sat down twice. The inside leg matters more than you'd expect too, an inch or two either way changes the whole thing from relaxed to accidentally brief, so check that before the waist measurement even. They're at their best from late spring through to the end of summer, for the in between days that aren't quite pyjama weather but aren't a proper going out day either, sitting around at home, the school run, a warm evening when jeans feel like a punishment. If you've got none, start with a mid weight cotton jersey rather than anything too thin, the thin ones cling and show every seam of whatever's underneath, and nobody needs that information. A heavier jersey holds its shape, drapes rather than clings, and doesn't go see through the second the sun comes out, which happened to me once in a pale grey pair and I still think about it. Go for a length that sits just above the knee if you want them to double as something you could answer the door in without a conversation about it.
Once you've got a decent pair they go with almost anything you already own without you having to think hard about it, an old t shirt, a vest, a shirt left open over the top, trainers if you're going anywhere, nothing if you're not going anywhere at all. They're not a statement, they're the thing that lets everything else be comfortable, which is a different kind of useful than people give it credit for.
Reach for them on the days you want to feel put together without actually trying, which, let's be honest, is most days.