When you set clear limits for your child, you are:

Keeping your child away from people or things that might be harmful. Stopping hurtful behavior by the child. Promoting your child’s cooperation in family life.

A limit should tell your child what is expected, when and how well. Make your directions specific. Decide what you want your preschooler to do before giving directions. Tell your child in simple words. For example, “Every night, after we finish eating supper, you are to take your plate, glass, and flatware over the sink,” lets the child knows exactly what to do. In contrast, “Clean everything up after supper,” is vague. The child doesn’t really know what is expected.

Emphasize the Positive

Children learn the limits better if you emphasize the positive. Tell your child what to do rather than only what not to do. For example, you might say, "There are many breakable things in this store so please walk carefully and keep your hands to yourself." This is more pleasant and more helpful than, "Don't break anything."

Avoid the Negative

If our speech is loaded with negative words (no, don't, stop it, quit that, cut it out, shut up), our children may tune us out. For example, suppose a preschooler hears "don't touch the cup, don't touch the coffee table, don't touch the flowers, don't fool with the radio, and don't go near the stove." The child may decide that it is dangerous to touch anything and become uninterested in exploring and learning. Or the child may decide that adults just say "no" and that the way to deal with them is to touch as many things as possible. The child may not know that the "no" about the cup full of steaming coffee is more important than the "no" about the flowers and must be obeyed. When you restrict your use of strong negative words to situations of great importance, your preschooler is more likely to hear and obey them.

Dealing with Emotions

Setting positive limits is especially important for helping children deal with their emotions. When your child becomes angry and acts destructively, you are likely to think first of negative limits: "Don't talk to me like that!" "Don't hit your brother!" But, what do you want your child to do? You might say, “Instead of pushing your brother, ask him to move.” Or, “When you get angry, tell me how you feel. Say, ‘I’m mad.’”

Use more Do’s than Don’ts

Tell your child what to do rather than what not to do. Using DO’s rather than DON’Ts requires thought and practice. However, the improvement in your relationship with your child will make it worth the effort. Treat your child with the same consideration as you do when you talk with your friends.
DON’T forbids a behavior, but it doesn’t teach a child the right way to do things. Worse, it can lead to a negative relationship between parent and child, a relationship that seems always focused on what the child is doing wrong. Saying DO rather than DON’T can be the antidote.
There are two different types of DO’s – the teaching do and the redirecting do.—Teaching DO’s give instruction to your child. Use this DO message to teach your child what to do. —Redirecting DO’s can be used to distract your child. Rather than saying DON’T to the current activity, offer your child another, more acceptable activity.
Use DO statements to make your message to your preschooler clear and positive. Examine your limits.

Power of Using DO instead of DON’T

A parent wrote on an Internet parent blog that her daughter was about to pick up a cigarette butt. Instead of saying, “Don’t,” mother said, “Yucky. Step on it.” This redirected the action and is something her daughter now does every time she sees trash. The mother went on to say that she extends the concept to taking dangerous objects away from her child. When her daughter had the infant Tylenol bottle, she picked her up and took her to where they were going to "put it away.”