When NO has meaning

You should not introduce the word "NO" to your infant very early . I mean when they just start moving around and  exploring  . You should create a safe space that will allow your infant to explore freely. No should not be your child's first word as she does not understand what it means. I feel that "No" should be introduced at 14 months . Your baby has had a lot of time to freely explore without fear,she has been allowed to take risk. At 14 months you can now begin to set limits . When you "NO" it will have significance . You should also explain to your  baby why it is not safe for her to  undertake that action.
Here you are laying the roots for cooperation. Your baby will begin learning what is right from wrong,she is learning how to follow rules. When you say  "No" you should not scream it  as that will cause your baby to become anxious.You should use a low tone.Remember that young children learn from consistency and repetition. You must have patience as  these are all new skills that your baby is learning.
These skill are needed for school and should be taught during the infant/toddler years 0-3yrs old.
My grand son is now 14mos and now when you say to him"no" you cannot go up there and we remove him from the  space the next time the he gets close to the space he  stops ,looks at us  and we will say no that is dangerous. He walks away from the space.