You should dress respectfully as Bhutanese dress up formally when they visit Dzongs and temples, and they expect foreigners to do the same. You should wear long pants (even if jeans), shirts with full sleeves, and more formal skirts below the knees when you visit those places. Hats and shoes are not permitted inside Dzongs and temples.
Tight and revealing clothing is not suitable for general touring in Bhutan. Shorts and skirts are also not recommended for general touring, as they are uncomfortable to wear in the mountains or hills of Bhutan. Otherwise, jeans/slacks and a blouse or shirt is acceptable attire for most tourist sites. Respectful casual wear is fine for general touring in Bhutan.