When we were at MGM for EMH last week, RnR had huge lines almost immediately at opening whereas ToT was not as bad (relatively speaking). I'd get a FP for RnR, ride ToT, then ride RnR. That way you have finished all you want to do in that corner of the park. Like the previous poster suggested, you can then get a FP for Mermaid, do the Muppet show and double back for the Mermaid show. Mermaid also had huge lines the entire time we were there so I would FP that one for sure. After that you can hang out, take in some character greetings (there were lots of characters out around the square under the Sorcerer's hat), etc without stressing out.
Have a terrific time!