Use air-conditioners smartly.
Maintain it at a comfortable 23˚ C in summer - once on, all windows and doors should be kept closed.
Otherwise, if you don't have an air conditioner:
Dress for the weather - wear short-sleeved and loose-fitting clothes made from fabrics that breathe and absorb moisture and wear sandals whenever possible.
Insulate your home. Fire retardant ceiling insulation makes a home up to 10˚ C cooler in summer.
Install shade awnings on the outside of windows facing the sun - it reduces heat from entering your home.
Open windows and doors to allow cool breezes to circulate freely.