Use an age-appropriate car seat. Babies belong in a rear-facing seat until they're at least 1 year old and weigh 20 pounds. Recent research shows it's safer for them to stay rear-facing until they reach the car seat manufacturer's height or weight limit (usually when they're between 18 and 23 months).
Try out a new seat to make sure it secures easily. Also take your current seat to every test drive.
Make sure your car seat is installed properly. Visit www.seatcheck.org to find a car seat technician in your area, or go to www.chop.edu for instructions on using the LATCH system (lower anchors and tethers for children).