October is the perfect month to visit! That's when I went, the weather was very mild. Warm in the day & cool at night. Are you meeting any friends there or do you know anyone in Tokyo? That would be so helpful if you did. Like I said earlier, no one speaks English there, so it's very hard to communicate or get help unless you're at your hotel.
These are my three favorite areas of Tokyo
Asakusa (Cool temple & street fair)
Akihabara (anime / manga central, maid cafes, Yodabashi mall, capsules stations with used undies! lol!)
Ikebukuro (cool for shopping & malls, Sushine City mall is worth a visit, there's a super cute / weird indoor theme park called Namja Town - all about cats, one of my favorite places I went)
if I think of more I'll let you know. I went with my bf and we explored many different areas, their train system is pretty easy to understand.