As parents we tell our children "no" a lot. Those "no" answers are because we're tired, distracted, or have reached decision fatigue.
There are times when we need to say "no" to our child, but more frequently than not, there are times when we say no that we can say "yes."
Determining when we can say "yes" to our children's requests will help them gain confidence and strengthen your relationship.
When you're saying "no" to your child, ask yourself these questions about if you can say "yes."
Is it safe? Is it reasonable? Is it best for my child? 
If you can answer "yes," it's okay to change your mind and to change a "no" answer to a "yes" response.
There will be times when "no means no," and your child needs to accept that, but you also have to be able to enforce it. A child knows when a "no" answer doesn't mean "no."
Using the skill of Preventive Teaching helps you prepare your child for getting and accepting a "no" answer.  
You can learn more about the skill of Preventive Teaching at SmarterParenting.com.