In the following sentence what would be the correct punctuation
One more thing don't tell anyone about our conversation.
Should "One more thing" be separated by comma, dash or colon? Or perhaps nothing at all?
The simplest and the one I would prefer is to treat it as two sentences:
This also gives you the facility to maneuver the second part.
Where the second part is short, and more important, use a colon to direct attention:
Where the whole thing is rather simple and short, just include a comma:
[EDIT] additional info, the em dash.
A sentence like that would not be appropriate in formal writing at all. If you are reporting it as direct speech, a comma after thing would represent more or less accurately the way it might have been delivered.
All three are fine in informal writing. I prefer the first.