When do we start disciplining our kids? And what method is good? My baby is going to be 9 months. Is it too early?

My gal is 9 months too and I have started to discipline her by telling her a firm No whenever she screams for fun or when she like to pull my hair or touch things she is not supposed to touch. I read that we can already start disciplining them at this age but they will not understand fully yet. They may understand that the tone is different but they will still need to be distracted in order for them not to continue with the bad behaviour. It is never too early to set in place rules and boundaries so I will say go ahead and staff disciplining now but don't expect that they will understand.