Hello!
It will depend on your budget and where you want to live. Some people are trying to survive on 100,000 yen a month, some have companies that give them a 1,000,000 yen or more per month housing allowance. Some people want to live in Roppongi so they can hang out with gaijin every night, some want to live with the locals in Kichijoji.
Maybe you'll get better replies if you share where you want to live and how much you want to spend?