There’s a thread from last year with some great suggestions. I went with my wife last year. Be prepared to walk, it’s the best way. I would recommend the 911 museum, very emotional.
Some highlights for me
The Highline
Katz’s deli
subway to Brooklyn, then walk across the Brooklyn bridge, best at dusk, the view is amazing
nice restaurant/bar at the bottom of the Rockefeller
Walk around Central Park - there’s a nice bar near the entrance (Times Sq end) can’t remember the name but great for people watching
will probably think more later but it’s the best place!