Babies, specially the one that can crawl or stand up and walk, are unpredictable. You need constant supervision in order for them to be safe always. Sometimes we forget about them and they go to some parts of the house and endanger themselves. We need to check all over the house for potential threats like the staircase, kitchen, living room, etc. and do some necessary actions to prevent accidents. I cannot mention all of them but I will state some of my tips.

Staircase - try to put some sheet of plywood or any other wide objects to prevent them from climbing up or going down the stairs. Make sure it is the same height as the baby.
Kitchen - always check the place where you put your things. Put objects like knives, scissors or saucepan in a secure place. Do not put things on the edge of anything like table because it might fall and hit your child to the head.
Living room - check if the TV rack and TV set is securely fastened to the wall. Babies has the potential to climb there and their weight sometimes makes the TV rack or the TV set fall down crushing them.