1 day must-dos

Hi, I have a trip coming up, and I already have some things on my list. But what do you think would be a must-do for 1 day? For example, if I were in Tokyo and had to visit spots X and Y, which are fairly doable in a day, what would that be? I feel like I'm all over the place trying to go to Akihabara, then Ueno, then Shinjuku, etc. I want to focus on a single day (for now) and determine what's a must-do. Thoughts?

by willster816