Finding a place in London

Hi all,
I am currently living in Cardiff, I am looking for a room or small flat for a reasonable price in London. If anyone has any suggestions including areas specifically to avoid I would be grateful.

I am currently working as Freelance reporter but I am looking for a better position within the City. And on top of it my current location is about to become unavailable in a week so I am debating just moving to London rather than continuing to make due in Cardiff.

Any suggestions would greatly be appreciated.