Monochromatic neutrals. They're pleasing to the eye, it looks elevated, and it's less fussy about what goes with what.
Short-sleeve layering: when it's too hot to layer with a blazer or jacket (the ultimate in pulling a look together) then try cooler alternatives like a short sleeve linen shirt that you leave unbuttoned, like a jacket.
Remember the finishing pieces! Don't forget to choose sandals with style over casual flip-flops. And be sure to add jewelry to pull it all into a cohesive look.