Head to one of the city’s main museums, such as the Museum of Natural History or the MoMA (Museum of Modern Art). Both are always full of people, many of which are locals visiting on their own, which will give you plenty of chances to start a conversation or to simply walk around surrounded by people.
Have a coffee at one of the many outdoor cafés in The Village or SoHo, in downtown Manhattan. These are great places for people-watching and also for shopping for souvenirs, knick-knacks or second-hand clothes.
Walk down Fifth Avenue and fantasize about the things you would buy if you were a millionaire. Stop by famous stores such as Tiffany & Co., Bergdorf Goodman, Saks Fifth Avenue and Prada. Even if you can’t afford to buy anything, you can still enjoy the views and try on things.
Book a hotel near one of the most active points of the city. Times Square, 34th Street and Columbus Circle are all hops of activity all year long, so you’re likely to find something to do and see as soon as you step out of the hotel. Most hotels facing Central Park are also busy and basically near all attractions and transportation.
Go to the theater. It’s one of the few activities in which being alone is actually a plus. Broadway tickets can be found at a large discount at the TKTS Discount Ticket Booths. The TKTS booth on 46th Street and Broadway is the one closest to all the theaters.