Concentrate on the visible bits. Eyebrows should be tweezed, threaded, shaped (and tinted if necessary) and brushed into place with a spoolie every day. Your nails should be cleaned at every opportunity, and if you have time for polish a basecoat and a top coat without colour is very natural and very chic, as long as the nails are clean. I prefer to see my own toenails with colour on them because I like open sandals in summer: first pro paint today and they are daisy white, because my feet are already a bit tan and it goes with everything.
I like casual for hair in summer, but mine is casual all year because it's grey and curly and the less I seem do to it, the better it is. Sadly this involves a ton of work and product to achieve an artless tumbled walked-off the beach looking this way, but a decent stylist and the right colour will see you nine-tenths of the way. I only use a hairdryer if the temperature is sub-zero as all I get with one is frizz.
I use a salt scrub once or twice a week on legs and KP zones, and cool showers are stimulating and refreshing, and dry skin out less.
It's more comfortable to wear light loose clothes in the heat than to show more skin. In the country, I mostly wear shorts in good weather, skirts in hot weather and Teva sandals for walking the dog, daily. No skin on view between the collar bone and elbow, or above the knee unless you're at home stretched on a deckchair or gardening or playing with DC or DGC. Sun screen on all the exposed bits. A sunhat that suits you.
Lots of water, salad, fruit and veg... they all hydrate you.
Sorry it's all boring routine you have been told several hundred times, but it works and you don't need to shop much for it, although a new outfit always gives me a perk too.