The thing that sends me back to the same few pieces isn't a date or an occasion, it's laundry day, when everything decent is in the wash and I'm stood there in something with a dead elastic band and a wire poking out the side. That's when you realise which bras and briefs actually earn a place in the drawer and which ones were a hopeful purchase from three summers ago.
Good lingerie sits underneath whatever you already wear rather than fighting it, so it pairs with more than you'd expect. A smooth, seam free bra disappears under a fine knit jumper. A simple bralette does the job under a slip dress when you want shape but not structure. Briefs cut without a thick waistband won't show through soft trousers, and a set in a colour close to your skin works under anything pale or sheer, which matters more than people realise until they're stood under shop lighting wondering why their bra is announcing itself.
How it wears depends entirely on the fabric. Cotton blends are forgiving, they hold their shape through repeated washes and don't go thin in awkward places, but they can lose a bit of softness if you tumble dry them, so I'd always hang them to dry. Lace is a different story, it's gorgeous but it snags, so anything with delicate lace work wants a lingerie bag in the machine, a cool wash, and no fabric softener near the elastic, because softener is what kills elastic fastest, not wear. Satin and silky slips need the gentlest cycle you've got, or a hand wash if you can face it, because heat and friction dull the sheen quickly.
If you're starting from nothing, I'd buy a well fitted everyday bra in a neutral shade before anything lacy or black, because that's the piece doing the most hours in your week. Add plain briefs in the same tone next. The lace sets and the black pieces are worth having, but they're the second wave, once the basics are sorted and actually fit properly.
Plain, well made pieces suit every season and most days, under work clothes, under gym kit, under a wedding outfit in June. The lace and the sets come into their own for evenings that feel a bit more deliberate, anniversaries, a weekend away, the sort of night you've actually planned what you're wearing underneath as well as on top.
Get the shape right underneath and even your oldest jumper sits better than it did yesterday.