Post a brief tip in the middle of the screen each time a transcriber logs on. The tip could be a frequent transcribing error and the way to correct it. Could be a different one for each log on or change it once every few days.
Another suggestion: I don't have the patience to try to decipher some headstones. I know that I can mark some as unreadable but others may be readable, but not by me, so I skip them. If a lot of other people skip the same headstones, is there a way to log this and take them out of the loop? If you can determine people who like to decipher difficult stones, maybe you could send those images to those people.
The new transcribing process is a great improvement!