A bit late to reply, but thought I'd add my 2 cents. I would completely agree that "tell you something good" is not the best translation. How I translate it would be mostly based on what follows. If it was a relayed secret, I might use "Here's something juicy..." If the phrase was simply a "character-flavoring" repeated by a single person, I might render "I'll tell you how it is..." or "Here's a good one...".
Generally I take the sum-total of the speaker's lines (aka their personality) and let that guide the phrasing. A 100% literal translation often breaks characters, or as they say, 'a translator is good for legal contracts, but for art you need an interpretor'.
I recall a similar situation with the literal phrase 'Strange Tower'. I rendered "Dark Tower"; different words, but overall more accurate to the original, I believe.