Make sure the car seat is not listed on any recall notices. Check reputable consumer Web sites like recalls.gov for that information.
Read your car's owner's manual and the child car seat instructions carefully. Look for labels on the seat as well.
Follow this rule of thumb: Babies belong in rear-facing car seats until about age 1 year and at least 20 pounds. At 20 pounds, turn the restraint around so that it faces the front of the car. Kids over 40 pounds should be in a booster seat until the seat belt fits properly without it.
Ask a car dealer whether you need an attaching belt or top-tether. In cars in which the seat belt is mounted to the door frame, this is needed because the belt won't tighten around the seat properly.
Remember that the safest place for a car seat is in the center of the rear seat.
Place the car seat in the car in the correct position for the child's age and weight.
Put the seat belt through the correct slot. The belt should remain tight while securing the seat.
Use a locking clip if the seat belt tightens only when you hit the brakes. This is a metal clip that attaches to the seatbelt. One should come with every new car seat.
Wiggle the seat back and forth. It shouldn't move more than an inch in any direction.
Buckle the harness over the child with the straps going over his or her shoulders. You should be able to put only one finger under the straps at the child's chest and collarbone.
Put the harness retainer or chest clip (if the seat has one) at armpit level. This holds the straps in place.
Be sure the harness straps are in the correct slots for the child's age and weight.
Ensure that all of the straps and belts are flat and not twisted.
Wedge a folded towel under the front of the seat if the child's head drops forward.
Tuck rolled-up blankets around an infant to keep him or her snug in the car seat.
Consider signing up for a car seat installation workshop. Ask at your local fire department.
Have your installation inspected. Check the National Highway Traffic Safety Administration's Web site for help finding an inspector (nhtsa.dot.gov).
Make sure you have not made these common mistakes: seat turned forward-facing before child is 1 year old and 20 pounds; seat belt not holding seat tightly; harness straps not snug enough or routed correctly; harness retainer clip above or below armpit level; locking clip not installed properly; seat belt not locked; babies put into rear-facing seats in front of or next to an air bag.