What are some tips for creating a safe nursery?

Safe crib. An approved safe crib 1st. Make sure all toys are safe. Avoid window treatments with cords or drapes that can smother. Ability to hear your baby either monitors or close proximity. A smoke and co2 detector is always wise.
Vigilant parents. There are a lot of products for "baby proofing" the house. Some, like stairs guards, are important in certain situations, but common sense and vigilant parents are the most important.