You don't give much info, like your interests or when you'd be traveling. But there is something in Tokyo for virtually everyone. Hundreds of museums, many places for shopping, over a dozen traditional gardens, several great places for city views, you name it.
For a first timer, the Sensoji Temple is just about carved in stone for everyone. If you go from late winter to early May, you can also see the Denboin Garden there, which is closed to the public the rest of the year. Meiji Shrine is also very popular among new visitors; the shrine is fine though not Japan's best, but the shrine garden is quite good and mostly ignored by the mobs of tourists streaming past it. In fact, it's hard to believe you're in one the world's biggest cities when you're in it.
Another important detail is if you are also going elsewhere while in Japan, such as to the Kansai Region, or your time in Tokyo is your whole stay. If the latter, for a more well rounded experience, after about 3-4 days in Tokyo you could get out of the city for a day trip - there are dozens of choices, like Nikko, Kamakura, Karuizawa, Chichibu, Hakone, the Fuji 5 Lakes, etc.
You can do yourself a big favor and figure out what appeals to you the most, and then going to the best places for it. If you just wander around cluelessly, you might, if lucky, squeeze out enough novelty to think you had a great trip - but in reality you will have missed a ton of great places.
You can start by looking at the resources below:
https://www.japan-guide.com/e/e2164.htmlhttps://goo.gl/qyQtGVhttp://www.gotokyo.org/en/