It's difficult to comment, without knowing how you're travelling - luxury package or economy backpacking? But my first tip, either way, would be to get a good guide book - personally, I favour "Lonely Planet" - and ensure you get off the beaten track (and away from the tour guide, if there is one) from time to time.
Next, and perhaps controversially, try not to be too affected by the poverty and deprivation you'll see all around you. Note, rather, how people who are desperately poor by western standards still manage to lead fulfilling and enjoyable lives.
Third, more practically, if you're eating at local places, choose the most popular, rather than those that look "nice" - the food is more likely to be freshly cooked and therefore kinder to your tummy.