New child seat standards will be phased in over the next three years. Meanwhile, some National Highway Traffic Safety Administration tips:
*Children should always ride in the back seat, and whenever possible in the center of the car.
*When you grab the seat at the slots where the belts hold it, it should rock no more than 1 inch side-to-side. The top of the child seat should pull no more than 1 inch away from the seat back.
*To get it tight enough, put your weight on the seat to press it down as you tighten the seat belts.
*Infants less than 20 pounds and less than one year old should ride in a rear-facing child seat. When children reach 20 pounds and one year, they can face forward in a car seat. Above 40 pounds, children can ride in a booster seat.
*Children should not ride in any seat with an active front or side air bag.
*Child seats should not be attached with a belt that can reel out after it is buckled, such as most shoulder belts. Passenger shoulder belts in many cars will lock to secure a child seat when you pull them out all the way and then retract them. The belts will click every inch or so as they retract to indicate they are in the locking child-seat mode.
*Seat belts that won't hold a child seat tightly may require an accessory locking clip, provided with most car seats, that won't let the belt slide. To attach the locking clip, buckle the seat in tight, hold the buckle in position along the belts, and release the buckle to get some slack. Then fold both the lap and shoulder belts into the clip on top of each other and rebuckle. The locking clip should be as close to the buckle as possible.
*With old manual-cinch lap belts, make sure the latch plate (the male end of the buckle) lies flat when it is buckled, not at an angle. If you can't get the belt tight enough without the buckle bending over the child-seat slot, turn the latch plate over 1/2 turn and buckle it upside down so the belt goes flat over the bottom of the latch plate before turning to go through the seat.
*Tighten the harness that holds the baby so you can't get more than one finger under it.
For more info
National Highway Traffic
National SAFE KIDS Campaign