Tell your children what you want them to do instead of telling them what you do not want them to do. This will give them clear directions and clarify your expectations in a positive way. For example: Say, "Pick up your clothes and toys from your floor and put them away." instead of "Don't leave your stuff all over your room." Or, "Leave the light off." instead of "Don't leave the light on."
Little changes can make BIG differences. Try it for a week, or even a weekend, and let me know how it goes!