不管是it's not good 还是it's bad,
to 的後面接动词---"做"什麼不好：
"it's bad to smoke/ it's not good to smoke" =抽菸不好
for 的後面接名词---"对"谁或者什麼不好：
("it's bad for your health/ it's not good for your health" =对你身体健康不好)