how do you dress to be the heat

[Twin]

WalMart sells a version of the "HeatGear" shirts for $12.99.  I got a couple of them and wear one under my cowboy shirt.  It works just as well as the $30 Nike version I have.

[Marshal Tac]

I am a full time cop and Range Master in Arizona. I spend a lot of time in the heat, and a lot of time wearing body armor under my uniform. One of the best ways I have found to avoid the heat rash that is common with cotton t-shirts trapping the moisture against your skin is to wear the "Under Armor" tight fitting "Spandex" type under shirts as my first layer, then my vest, then my uniform shirt. The same style shirt is sold at Wal-Mart for about $13, as stated before. It wicks the moisture off of your skin and puts it outside the material to evaporate better. I also wear this type of under shirt beneath my cowboy clothes when its hot out, for the same reason. It works even better under my shirt without my body armor on. Make sure you get the type that are tight fitting. You should have to stretch it to put it on. If it's loose, it will not be as effective, as the sweat will not contact the cloth in some places. I wear the sleeveless style, as they allow for more freedom of movement for my arms. (Important when shooting)

I also wear one of the "Polymer crystal" neck ties that is soaked in cold water and swells up then evaporates the water when worn, like was mentioned earlier. This neck tie works well in the dryer humidity here in the desert, but may not have as much of an effect in the humid areas.

In my cowboy clothes, I also wear a light colored breathable cotton shirt over my under shirt, with the sleeves all the way down and I put a cold damp hankerchief inside my hat (I am bald, so no hair do to worry about, and it keeps my sweat from running down into my shooting glasses).

My pard who shoots holy black, swears by it cuz the smoke makes SHADE! 

Give the undershirts a try.

[Delmonico]

That is why wool underwear was worn so much even in the summer, it wicks away the moisture.  This is a good thing in heat and in cold.