If you are coming on the east-west, blue/green lines, exit at Five Points and follow the signs to street level then to the Peachtree Street exit. Turn left onto Peachtree Street and walk about two blocks to get to Woodruff Park.
Otherwise, if you are coming from the north or south, you can also exit at the Peachtree Center Station. Follow the signs pointing to the Ellis Street/public library exit. After exiting the turnstiles, turn left and either take the elevator or escalator up to street level. At street level, turn left to walk along Peachtree Street. The park is about 1.5 blocks down on the left.