Positive language ensures that children do not tune out your words of discipline. For example, telling a child to sit the cup on the table, instead of "don't play with your juice" is likely to have a greater impact on a child's learning appropriate behavior. Focusing on "do's" instead of "dont's" will help children to focus on the right thing to do, rather than the wrong things they are doing.
Develop reasonable limits that matter, instead of trivial issues to cater to child's age and development level. Tell your child to be respectful of other classmates, for instance. In this example, the focus is not on a variety of ways a child can be respectful, but is rather on the broader concept of being respectful. To reinforce this concept, ask the children how they can be respectful of other classmates, and they will set their own rules.
Do not ask children general questions, such as "What do you want to read today?" Instead, ask "Would you like to read Book A or Book B?" The former is likely to lead to problems, as your child cannot make such decisions in a reasonable manner. You can apply this idea to a child who forgets to clean his space, as well. Ask "Would you like to clean your desk now or clean the chalkboard for the rest of the week?" Doing so will enable him to take ownership of the commitments he has made to you, as opposed to simply being told what to do.