I've been trying different opening words, and I saw an article at CNET that suggested ROATE might be the optimal opening word. So I decided to try it.
My second guess was focused on on testing vowel locations, along with including a couple of common consonants.
After guess 2 it seemed straightforward, since the word had to be in the form C__AO. And CACAO was the only word I could come up with that met that pattern.