As little as possible as it will be the hottest month. Where i am it is also humid.
People are all shapes and sizes and no one bats an eyelid at upper arm circumference or thighs in shorts (as long as they're not right up your bum!).
Linen may be unfashionable but it is a godsend in this heat, the naturally crinkly-looking stuff.
Wear natural fabrics as much as possible, anything slightly poliester/viscose etc will make you feel like you're melting.
I wear short-sleeved tops/tshirts mostly from h&m, one or two from zara. I avoid strappy tops as i don't have the prettiest skin on shoulders/back.
I have a handful of maxiskirts (oldest i bought in 2002) and prefer them to knee length or short skirts (the faff of shaving 
).
Bring enough clothes that you can change twice a day, if possible, even though i'm accustomed to the heat i find i have to change clothes after lunch! Bring a shawl for overly airconditioned restaurants. It'll be super hot enough to eat outside every evening.
If you buy sandals for your hols, try and wear them in before your holiday as new shoes + hot slidey sweaty feet = minging! You can buy compeed blister thingies from pharmacy or little shops called Clarel.
Enjoy!