What I actually check before putting baby down for the night:
Baby is fed (if haven’t been fed for a while)
Diaper is changed. I have been using overnight diaper since 4 month. It is really really helpful!! Previously, if I changed a diaper in the midnight, she may wake up and cry.
Comfortable sleepwear. I usually put footed pajamas on her in case her feet get cold during midnight.
Safe sleep space. It is recommended by pediatricians that no blankets or pillows on the bed.
Room temperature checked, 68-72F as recommended by pediatricians.
Baby monitor turned on and adjusted.
Mom has water or essential stuffs nearby! If you go and grab something in other place, it may wake up the baby. So I usually put essential stuffs near by~
By the way, if your baby occasionally fall asleep on your bed, make sure you put something around her to prevent her dropping from bed suddenly. Baby moves so fast!!
Any other things in your mind?
I hate the dark and don’t like rooms too dark. 
I swear the second I get comfortable and realize my water or something I need is across the room, baby suddenly wakes up lol. I also love having a little routine before bed because once you’ve checked everything you can actually relax a little bit more. And footie pajamas are my favvv, those tiny cold feet will have me checking on them 100 times 