You Must Be Consistent - If you decide to lay down a law/rule you must have the self discipline to enforce it with real consequences. If you don't enforce the law how can you expect a child to respect it.
Tips and Tools - Encourage yourself to be consistent by rewarding yourself. Parents need to be rewarded too. Decide where you would like to go for a weekend away and pop a postcard on the fridge to remind you where you will be going after a whole month of being consistent.