There are tremendous things to do in Tokyo, from traditional to futuristic depending on your interests.
If you like traditional, visit shrines, temples, and Japanese gardens. There are many famous and beautiful sights you would want to check out.
If you like to go futuristic, visit technical museums like Miraikan, or walk around downtown such as Shinjuku and Ginza.
If you like to shop, there are many districts in Tokyo with lots of shops such as Ginza, Shinjuku, Shibuya, Harajuku.. etc.
However, I think the most attractive part of exploring Tokyo is food, I think. Try different cuisines, traditional to international! You would be amazed by its taste :P