We recommend allowing yourself at least a semester to adjust to the new challenges and rigors of college. Your academics are your first priority, so if you're struggling to maintain a solid GPA, adding an internship on top of everything else is not the best idea.
However, if you feel you can handle the added work of interning on top of your other responsibilities, then the second semester of your freshman year is a good time to start looking for an internship for the summer or fall semester.
Finding an internship takes time. Allow yourself an entire semester to find an internship that fits your goals and schedule.