Safe, polite way to remind a professor of something?

I am not a native English speaker.

From time to time, when I have to send a reminder email to professors, say my advisor, I feel embarrassed in phrasing. Usually I choose "Please be informed that ...", but later I found this may be too formal and mechanical (is it?)

Thus I am after a polite, not imperative, and not too formal substitute way to remind a professor via email.