when should I take psat sat act and sat2

<p>Im a freshman with a 4.0 gpa and ranked 1st in my grade (I dont know if this matters) .when should I take psat act and sat? Should I start sat as a sophomore or what? I know that Harvard requires sat2. Im interested in law and biology as well as mathematics ( I know completely unrelated) what and when should I take these sat2s?</p>