Nick Stahl to Amanda Bynes -- Wanna Get Better? STOP THE TWEETING

Formerly troubled "Terminator 3" star Nick Stahl has some invaluable words of advice for Amanda Bynes ... if she wants to turn her life around, she should start by pulling the plug on her crazy Twitter account.

Stahl -- who famously struggled with drugs, alcohol and other personal issues in the last year -- tells TMZ Amanda's habit of constantly chronicling her every waking move isn't healthy ... and she should spend her time reconnecting with friends and family instead.

But Stahl's still optimistic, adding, "She'll figure it out. She's young."