The first word most Toddlers hear and say is "NO". "No, don't touch that", "No, don't climb that", "No biting", "No hitting", NO, NO, NO! Toddlers main focus is to explore, they are discovering new things, and are curious about the world and everything that surrounds them. Your job is to keep them safe, but they stay in the way of trouble.
If the word "No" is used too much, it loses its power. Most of the time saying no makes your child do the opposite of what you ask them to do. The best advice is to eliminate the word "No" and exchange it with positive words. "No hitting" changes to " hands are for high fives, and hugging", "no biting" changes to " teeth are for eating and smiling", and "no running" changes to "walking feet" and "Let me see you march". There's power in what we say, and how we say it. Of course it's not easy to stop saying "no" right away, but changing a few simple words makes your child do what you want them to do.