Ah, the life of a preschooler: finger paint, playgrounds, puppets and picture books -- and rules. Yes, rules. Children thrive in an atmosphere that has clearly established boundaries. Preschoolers need to know what is expected of them and understand the consequences for acting outside of the boundaries. Introduce rules to preschoolers simply, clearly and in positive terms, and use a variety of means to communicate.
Teach new rules during calm, neutral times -- not when you're in a rush or distracted by other activities. If possible, begin talking to your child about rules before you need to enforce them and expect to repeat yourself a lot in the beginning. For example, don't introduce a rule about behavior in church as you're dashing out the door trying to find shoes and socks. Be proactive -- remind little people to wash their hands before sitting down for a snack rather than scold them about dirty hands after they dig in to their crackers and juice.
Rather than inundate preschoolers with repeated verbal direction, reinforce rules with visual images. Place labels with images in places where they only need a simple queue to remember the expectation. Affix a small label with a photo of you on it reminds them that they need to ask for permission before using that item; a picture of sudsy hands just above the door knob inside the bathroom door reminds them to wash up before exiting.
Sing! Teach a simple song to accompany rules for hand washing, cleaning up or walking the dog. Kids can't resist joining into a catchy tune with simple lyrics and before they know it, they're swept up in the momentum. Instead of hollering at your kids to clean up after themselves, begin singing "Clean up, clean up, everybody, everywhere. Clean up, clean up, everybody do your share!" to solicit their help tidying up after mealtime or a craft project.