I cannot believe I have to fucking explain this...
Do NOT give your birds cigarettes (even if they are unlit) or alchohol. This should be a no-brainer but apparently some people are too fucking dumb to realize this.
Do not smoke around your bird. Or any other pets for that matter.
Do not leave toddlers or babies alone (unsupervised) with birds. They could injure each other and toddlers will most likely not know to not squeeze a bird (birds lack a diaphragm which means if you put too much pressure on their chest they will suffocate and die.) Your bird could also bite a toddler or baby which could (depending on the size of the bird and how hard they bite) really hurt them.
Do not leave cats or dogs alone with your birds. Even if they get along and play, cat and dog saliva could kill a bird.
Do not leave a bird out of the cage when you are not at home. They could get into mischief and hurt themselves.
Do not give your birds drugs and this includes caffeine.