This is advice from a guy with a PhD in Speech Pathology, specializing in stuttering: with the R sound, notice that it is a vocalized sound, meaning that your vocal cords are vibrating when you say it. This is opposed to letters like F, T, P, C, K, etc. where they are pronounced without the vocal cords vibrating. If you stutter on R, you are not vibrating your vocal cords, but you SHOULD be vibrating your vocal cords during an R sound. So if you notice yourself when you are speaking and your vocal cords stop vibrating during your next R word, remind yourself to let your vocal cords continue to vibrate through the R sound. Focus on maintaining vibration of your vocal cords through the words as you speak them. "THHRREEEE", ALLRREEEADDYY", etc. Hope that helps some