Must have written my big post as you were posting yours. Oops. Good to see you're on the right track now. Timing is everything, stuffing up your timing with rewards based training is more forgiving than other methods. Ie you've got more room for error, and if you and the dog can get it right 8 out of 10 times that's usually enough for the lesson to "take".
And what your dog finds most rewarding - will be different over time and depending on the circumstances. Some people keep lists... makes it easy. Sometimes it's hard to tell. I can put a ring of different foods around my dog to see which one she will eat first. And she just goes to the nearest treat or the one I put down first, even tho she doesn't get to start until they're all down, and hovers around the arc of treats. Does not go to her faves first.
I can only tell what she likes best by how distracting she finds it, and how hard she works for it.