Next to walking, the best way to really see New York City is on two wheels. If you've already shopped Fifth Avenue, checked out Rockefeller Center and seen the new Times Square, think about boarding a bicycle to visit other parts of town. You can ride a few leisurely miles in Central Park or take off across the George Washington Bridge and head north into country terrain. Or you can just set out on your own to explore the city. By far the best time to see the city on a bike is on the weekend, since the traffic is light.
Any direction is the right one.
But if you're starting in midtown, you need to have an idea of the distance you want to travel and the special things you want to see. One way to do this would be to ride up the west side. Get onto Riverside Drive at 72nd Street, take that up to 165th St., and go up the hill to Fort Washington Street. You might want to ride across and check out the view along the Palisades. If you want to keep the ride urban, go past the George Washington Bridge into Fort Tyron Park, ride around and start heading south, drifting eastward as you go through Harlem and the Upper East Side.