Be frugal when eating during your first days in here and prefer dishes that are not that seasoned or greasy. Likewise, avoid those places that do not show proper hygienic conditions. Regarding the fruits, prefer those that can be peeled, and in the case of salads only ask for them at the tourist restaurants provided they look clean.
Be also prudent with fishes and seafood, eat them only at places you regard as safe.
If in spite of all these precautions you were to suffer a stomach problem (a rather common malady amongst travellers), drink plenty of purified water and anti-acids after every meal. If the problem were to persist, consult a physician.
How can I avoid getting sunburned?
Bear in mind that the ideal way of getting a nice suntan is by exposing yourself first during short periods of time to then stretch them progressively to avoid your skin from being damaged by the sunrays. Try not to be too long under the rays of the sun king during the first days.
Do not fail to use sunscreen and to drink plenty of water in order to keep your skin hydrated. Do not hesitate to ask for medical assistance if you were to suffer sunburns or erythemas. Remember that the big hotels have health professionals working 24 hours a day.