Unfortunately I live in a humid climate - I can take 45 celsius in Las Vegas better than for example 28 celsius in Amsterdam. My tip, next to staying hydrated, would be wearing EVERYTHING cotton, from your shirt, pants to your very socks! It makes such a difference. Look for it when you're shopping next time. Clothes that have more than 10% of any form of plastic "worn" in it are guaranteerd to stick against your body; making you uncomfortable.