This is a serious issue at auditions, or if you’re called to fill in as an accompanist for a show or rehearsal at the last minute.
If you’re lucky enough to have one of your show’s assistant directors or your little brother in the room to turn pages for you, then you’re golden (assuming they can read music, or at least react quickly to a timely head nod. Actually, there are surprising number of people who can’t!)
But it happens more than ever so often that you’re stuck having to sight read and turn pages at the same time. In auditions the singer will often just plop the music in front of you, so you can’t do the earmarks-on-the-corners thing (if you’re one of those people who does that — I’m not).
I don’t have the full answer to this question, but here’s what I’ve learned:
1) My basic rule to try always to be reading a bar ahead applies doubly here. If you can, quickly scan the last bar or two (this is going to depend on tempo and meter) of the page before you turn it.
2) 99% of the time, it’s the bass line, hence the left hand, which is most important in guiding the singer. So make sure that if you hit anything, you get those bass notes in the last bars on the pre-flip page — especially if they’re on a downbeat (or whatever the basic beat structure is of a piece).
3) The worst situation is when multiple aspects of a piece change at the top of the post-flip page. And publishers love to do that, for some reason, maybe just to freak us accompanists out. You just always have to be wary of a possible change in time signature, tempo, or key… remind yourself every time you’re on the bottom staves of a pre-flip page that things could be really different on the flip side. This is just a matter of practice.
Those are my tips. But they still haven’t prevented the occasional disaster. Any other ideas?