Definitely a visit to the beach always works wonders, although we're not all fortunate enough to live conveniently close by one.
On outrageously hot days when even the air conditioning is struggling, I find a lovely cool bath is very refreshing. Otherwise, if I'm sitting around at home I'll fill a large bucket or tub with water and soak my feet in there. I find this works wonders. Jade's idea of filling a spray bottle with cool water and spraying it on herself is also one I try when it gets too hot for comfort. I like to add a small dash of rose water (which can be bought at most Asian and Middle Eastern stores), which I find is extra refreshing. Another top tip is to burn refreshing essential oils in an oil burner as this is very invigorating. Light citrus oils are best, in my opinion...orange, bergamot, lemon and grapefruit are my favourites.