Sometimes you just don't want to sound upbeat.
I get it.
The key to getting a high speaking score is to sound excited and enthusiastic. Sure, you've got to have your grammar, correct use of vocabulary, and content all in place too, but if you sound like you're bored, then your grader will also be bored. A bored grader equals a low score. So, get your intonation going on and sound UP! Here's a short video about how to use intonation on your TOEFL Speaking section.