Check with health authorities well in advance before you go, as you may need to take preventatives starting weeks before you set out. Good personal hygiene is a prerequisite to good health. Few public bathrooms have toilet paper. Carry some with you during your travels. If you can take the bottle top off or peel it, you can drink or eat it most anywhere in the world.
Dehydration is no fun.
Avoid excesses of alcohol and food, at least until your body starts to adjust to its new environment. Plan ahead and build flexibility into your travel itinerary. Reducing emotional stress as well as physical stress will enable you to adjust more quickly to your new surroundings - and maximize the probabilities for a healthy, enjoyable trip.