Take food as you would normally do. I mean only if normal is you are not the greedy one that piles your plate up with food and then leaves it untouched at the table. You might see some Thai doing that, too. You may see a different side of certain Thais in this situation, but ignore them just like all the other Thais would.
What about not putting more than three things on your plate? Well, put soup or curry in a separate bowl that they normally provide near the soup station, and put other food on a separate plate. I still try not to put too many things on it and instead come back for a second, third or fourth round. Thai food has so many varieties of flavors, I don’t like to mix them all in one serving. The general rule is don’t take too much, don’t try to put more than two or three things with gravy on the same plate, and don’t put fruits or dessert with the savory items.