。
If I were you, I wouldn't do that.
Literal
I [subject-が] you [if-なら], like-that [topic-は] don't-do [confirmation-ね].
The sentence-final ね invites the listener's agreement — 'right?' — turning what could be a flat declaration into a softer, conversational remark. Using ね instead of な shifts the tone from private reflection ('I wouldn't do that, I tell myself') to shared conversation ('I wouldn't do that, would you?'). 僕が君なら ('if I were you') is the standard counterfactual frame for offering advice without sounding preachy.