where to start tidying in a cluttered small apartment

i live in a one bedroom flat which is very small, and its very cluttered with stuff, possessions, paperwork, clothing in refuse bags because i don't have the storage space.....my mothers coming down for christmas time and she would be upset with me if she saw the mess my apartment is in right now...so i have to get it tidied before she gets here....but i feel overwhelmed and not knowing where to start?

any help?