The afternoon the light starts going soft and gray around four thirty, that's when I want them on. Not blazing yet, not the big show, just a warm string catching the last of the daylight through a window while everyone's still in coats. That first flick of the switch on a dark, ordinary evening in late November is most of the reason to bother with Christmas lights at all, before any tree goes up, before anything else about the season feels real.
They suit almost every kind of home differently, which is the nice thing about them. In a rented apartment with no mantel and no yard, a single warm white string along a window frame or looped over a mirror does more than you'd expect, and it comes down in ten minutes when the lease says so. In a family house they tend to spread, a string on the stairs, another round the porch posts, one more that someone's kid insists on for their bedroom, until you're the house with the fuse box doing overtime. If you've got none yet, start with one warm white string, plain and steady, no flashing settings, and a length a bit longer than you think you need so you're not stretching it taut round a banister. You'll add color or icicle lights or the big outdoor ones later, once you know where you actually want light rather than where you assumed you did. Against ordinary furniture they sit well with anything plain nearby, a bare branch in a jug, a mantel with nothing much else on it, a window with the curtain pulled half back so the string shows from outside too. Too much going on around them and you lose the point, which is just a bit of warm light in a dark room.
The difference between a good string and an annoying one is mostly in your hands before you even plug it in. Check the wire itself, not just the bulbs, rubbery and a bit thick rather than thin and brittle, because that's what survives being wound round a tree eight times and shoved in a box in January. Look at where the bulbs meet the wire, a sloppy, exposed join there is where strings die first, usually at the one bulb you can't reach once it's up. Bend a length of it gently. If it kinks and stays kinked, it'll crack outdoors before Christmas is done. Plug it in before you commit to hanging anything, every time, because finding a dead string halfway up a staircase is a special kind of bad mood.
Buy more length than feels sensible, you will always want to go one more loop round.