Socks used to be the thing you grabbed in a multipack without thinking twice, but that has shifted. There is now real attention to fit, to cuff height, to whether a trainer sock will stay put through a day of walking rather than working its way under your heel. On the whole that is a good change, even if it means standing in front of a drawer for longer than socks ever used to deserve.
If you are starting from nothing, go plain before you go patterned. A simple cotton ankle sock, not too thin, with a bit of ribbing at the cuff so it holds its shape rather than rolling down by lunchtime, will do more work in your week than anything with a slogan on it. That is the pair you wear with jeans and trainers on an ordinary day, under boots with thick tights underneath on a cold one, or with loafers when you want something that will not show above the shoe line. Once you have that sorted, knee highs are worth adding for skirts and dresses in colder months, and a black pack for anything smart, since black socks disappear under trousers in a way other colours just do not.
For colours to actually live with, stick to black, navy, grey and a plain oatmeal or white for underneath lighter trousers. These go with almost everything already in your drawer, which matters more than it sounds. Before you buy, check where the toe seam sits, because a seam running straight across the toe rather than along it will needle you by mid afternoon, and check the cuff for proper elastic rather than something that has just been folded over and stitched, since that is usually the first part to give up. A well made sock has a decent cotton content rather than being mostly synthetic padded out to feel thick in the packet, a reinforced heel and toe you can actually see and feel, and a flat seam that does not sit proud when you run a finger over it. A disappointing one goes thin at the heel within a few washes, loses its elastic, and ends up sliding down inside your shoe by midday, which is the one thing a sock is not allowed to do.
Start with black. It is the one colour that works with almost every shoe you own and shows the least wear.