First things first in terms of sweat–your pits!
Summer’s heat and humidity will make you sweat everywhere, but obviously, your underarms will be the biggest worry, because they have the most potential get stinky. Make sure your soap or body wash in the shower is antibacterial to kill the bacteria that mix with your sweat and make it smell funky! You may want to switch deodorants for the season to something stronger. You can look for antiperspirants and deodorants labeled “Clinical Strength” or “Clinical Protection” if you’re not using one already.
Another option would be to try out a rock crystal, which you can get at health and natural food stores. They block bacteria and therefore make you not get stinky if you get sweaty. Bonus? You can use them anywhere you tend to sweat a lot, not just your pits. (Bye bye, boob/back/cleavage sweat!) This also helps if you’re prone to heat rash.
If you’re really paranoid about your pits, you can pick up some sweat block pads. They’re cloths soaked in industrial-strength anti-antiperspirant that you can apply once a week to help prevent sweating. Underarm pads that you can wear in your shirts help soak up sweat, too, but obvs you can’t don those with your favorite tank.
If you get sweatstains on your clothes, soak them in cold water, preferably inside out, and use a stain fighter (they’re usually in sprays or wipes that go along with your regular detergent) to hedge your bets.
An important thing to remember: Go easy on the perfume in the summer months! Heat will intensify whatever fragrance you wear, so it’s easier than ever to overpower people with your scent. A little dab’ll do ya!