The best way is to never substitute words, as it will actually add to your problem. Just allow yourself to stutter. Eventually you will become desensitized to stuttering and you won't feel as bad, and your stuttering will lessen. You want to stutter foward. IMO, stuttering has its root in avoidance. Word substitution is a form of avoidance. Basically the first step is to get to the stage where you are allowing yourself to stutter openly, speaking forwardly, not using tricks, etc. Then you can start to work on your stutter, become aware of what you are doing when you stutter, and modifying your behavior. I'm 28 years old and only in the past couple years I realized all this. Running from stuttering or using tricks to avoid stuttering is a terrible way to live life. Check out the Stuttering Self Therapy book on Amazon for some great advice.