Food abroad. When abroad, try to avoid foods that come from the ground - i.e. fresh fruits/ vegetables, as they will be grown with indiginous water, and soil bacteria or other contaminants you have not been exposed too. Unless they are peeled. Most contamination will remain with the peel. This is the only time that you may NOT want a fresh salad. Of course fresh water is another thing to consider avoiding.
Many tips. Depends on where you're going. In developing countries, drink only bottled water. Consider bringing iodine tablets or a straw water filter - many brands available. You will have to balance adventure with personal tolerance of risk - fresh veggies and street vendor food are more risky for infection, but also delicious. Bring some Cipro (ciprofloxacin) (antibiotic) just in case. Hope this helps!