Overall, L.A. is a healthy place to visit, although people with respiratory problems should keep in mind that L.A.'s air quality can often be poor, particularly in the valleys in the mid- to late summer (too many cars, too little wind). When the air quality is really bad, warnings are aired on local TV and radio stations encouraging people to avoid outdoor activities. If you're concerned about smog levels affecting your vacation, you can contact the South Coast Air Quality Management District at tel. 800/CUT-SMOG (288-7664) or www.aqmd.gov, which also publishes "Air Quality Forecast/Advisories" for the greater L.A. region. Tip: If you want to avoid the summer smog, stay and play along the coast. The light offshore breezes usually keep the beach communities relatively smog free.
Also, for people not used to so much sun -- L.A. averages 320 sunny days a year -- be sure to protect yourself from the sun's rays by wearing appropriate clothing (long-sleeve shirts, wide-brim hats) and/or using sunscreen with an SPF rating of at least 30 and broad-spectrum UVA/UVB protection.
For a big city, Los Angeles is relatively safe, and requires only that you use common sense (for example, don't leave your new video camera on the seat of your parked car). However, in neighborhoods such as East L.A. and parts of Downtown (at night especially), it's a good idea to pay attention to your surroundings.
Avoid carrying valuables with you on the street, and don't display expensive cameras or electronic equipment. Hold on to your handbag, and place your wallet in an inside pocket. In theaters, restaurants, and other public places, keep your possessions in sight.
Remember also that hotels are open to the public, and in a large hotel, security may not be able to screen everyone entering. Always lock your room door -- don't assume that inside your hotel you are automatically safe.
Driving safety is important, too. If you drive off a highway into a questionable neighborhood, leave the area as quickly as possible. If you have an accident, even on the highway, stay in your car with the doors locked until you assess the situation or until the police arrive. If you're bumped from behind on the street or are involved in a minor accident with no injuries, and the situation appears to be suspicious, motion to the other driver to follow you. Never get out of your car in such situations. Go directly to the nearest police precinct, well-lit service station, or 24-hour store (again, having that GPS handy is key). Report the incident to the police department immediately by calling tel. 911. This is a free call, even from pay phones.
Parking: Better Secure than Sorry -- If you're driving to Venice Beach, pay the $5 to $10 fee for a secured lot, hide your valuables, and walk to the beach -- car break-ins aren't uncommon.