You can spot a good summer boot outfit from across a car park: ankle, air, and the boot doing one job instead of three. The bad version is a thick sole, a heavy upper and jeans bunched on top, and the whole thing looks like it's dressed for March and forgot to check the forecast.
Colour wise, tan and a soft sandy beige are the easiest things to live with, they go with denim, white, khaki, florals, almost anything you already own, and they don't shout about themselves in photos the way a bright white boot can. A worn in, slightly scuffed looking tan does more work than a pristine one, oddly, because it reads as lived in rather than brand new and trying too hard. Black has its place but it pulls everything a shade more serious and a shade warmer looking, which is the opposite of what you want in June. If you're drawn to pale leathers or suede, have a proper look at them in daylight through the shop window rather than under the lights inside, because what looks oatmeal indoors can look distinctly yellow once you're stood outside it, and a muddy festival or a sudden downpour will not be kind to pale suede at all.
These earn their place mostly from late spring through early autumn, anywhere there's a bit of grass, gravel or cobbles that sandals can't cope with. Garden parties, long outdoor lunches, festivals, a wedding on a lawn, the school summer fair if you've got kids, evenings that get cooler than the day promised. They're also the answer to the specific problem of wanting bare legs but not wanting your feet to do all the standing in flat sandals for six hours straight, ankle boots give you a bit more support without the heaviness of a winter pair. If you've got none of these yet, start with an ankle boot in a lightweight leather or a leather look, low block heel, nothing chunky on the sole, because that's the one that moves between a sundress, cropped jeans and shorts without any of them looking like a mismatch. Check the ankle for gape at the back when you walk, not just when you stand still, that's where a boot either looks neat or looks like it's slipping off.
Pair them with a slip dress, a denim skirt, or turned up jeans and a plain top, and they'll sit happily under most things you'd reach for on an ordinary morning. Tomorrow I'd put mine with a linen shirt dress and nothing else fussy at all.