Trying to not look like a tourist can be futile if you're going for the casual look and the advice I've heard from other frequent travelers is to go for the expat look especially in areas where you'll stick out due to your ethnicity.
White buttoned shirt, nice slacks, decent-looking shoes for men. I haven't been able to figure out a similar outfit for women but a decent-looking dress fitting for the climate and local modesty standards seems to be the best shot.