It really depends on what your interests are. If you have a friend that lives there, have them show you some of the hidden courtyard gardens that 99% of tourists don’t know about. If you like museums, there are plenty of those. Rijksmuseum (I consider it the Dutch Louvre), the Anne Frank house, the Van Gogh museum.. Vondelpark is one of my favorite places in the city, you can spend an hour or two wandering around and/or chilling out on the grass if the weather is cooperative.
Wandering around is pretty great, too.. the city is small enough to make seeing it by foot possible and you’ll stumble across beautiful architecture, statues, plazas. The tram system is fairly easy to navigate and you could also rent a bike, if you want to save your feet.
Lastly, watch out for bicyclists and don’t walk on the bike paths! They are super serious about the bike riding there and have little patience for the tourists who don’t get that. If you’re not careful, you could get mowed down or piss off the locals.