As a parent how often do the words ‘No’, 'Stop' or ‘Don’t’ feature in your vocabulary? How many times a day do you use them? What are the first words your child learns to say?
Re-directing your child can be the best solution, as it teaches her/him appropriate positive behaviour. For example: Your child is enjoying themselves by emptying your pot plant of soil. Instead of saying 'No' you could explain to them that we don't tip out the soil on the carpet and invite them to clean up before heading outside to do some weeding. You then provide them with their spade to dig up the weeds.
Another example: Your toddler is tipping their milk from their cup onto the kitchen floor making a mess. Instead of saying ‘Don’t’, you explain to them that it is dangerous and someone might slip over hurting themselves. Then you can invite them to help you clean up before playing in the kitchen sink or the bath tub with some plastic cups. Here you can show them how to fill up the cups and then tip out the water into the sink, making it an enjoyable experience.
Negative language confuses children and makes them feel like they are unable to do 'anything right'. It is hard for the child to understand what you really want them to do, if all you are saying to them is 'No', 'Stop' or 'Don't'. The best thing to do is to give them a reason why they should't be doing whatever inappropriate behaviour they are doing. Providing positive language tells your child to stop what they are doing and then do what you want them to do. Thinking about what you are about to say to your child before reacting badly, will give them a clearer picture of what you want them to do without confusing them or making them feel that they are unable to please you no matter what they do.
Toddlers and preschoolers haven't developed a high level of thinking as yet, so telling them 'No', 'Stop' or 'Don't is a pointless exercise because they already know just from those words what they are doing is wrong. Being particular about what you'd like your child to stop doing, and what you'd like them to do instead, takes away the uncertainty and confusion left open for your child's clarification about what they are doing wrong and what you want them to do instead.