Have you ever had a horribly messy roommate that you could not stand? Well read on to find out how to survive them.
Realize that they most definitely had a different upbringing than you and that they might not even know that it bothers you how messy they are.
Decide if you want to address the situation or just wait out your time until you can move out.
If the former, try to make them see the draw-backs to the mess. Ask them if they like bugs in the apartment, see how they feel about the lack of clean dishes because they are all dirty and smelly, and point out how unsightly the common areas you share are. Do this only if you are sure your roommate doesn't recognize the problem. Otherwise, they will just feel criticized, and may actually get dirtier in retaliation.
Oftentimes an effective method is pointing out that while you don't want them to feel like it's more your home than theirs, you both have a right to a comfortable living space. Messy, dirty and unhygienic doesn't work for everyone, but a (reasonable) amount of cleanliness works for everyone involved.
Recognize that they may want the house clean (almost) as much as you do, but it's just not as natural for them to clean as it is for you. Try to work out a system that works for both of you, and try to make it a team project as much as possible, not you against them.
Still, things might get a little heated between the two of you. This may be unavoidable, try to keep things constructive, and avoid outright bickering. If your roommate doesn't realize what will occur if they don't start picking up their end of the deal, then they will never be able to fix it and get better.
Now comes the process of splitting things that need to be done around the place in two, and assigning each of you jobs. Without firm and definite jobs, then some people will not realize that they were supposed to do something.
If you just want to wait, then you may have to adjust your attitude towards the situation and just keep your own areas of the place clean rather than try to change your roommate as well. If it seems unbearable, consider moving out.
If you are living in wardened accommodation or if your landlord is often on call, consider telling them if your roommate refuses to clean. It is often part of the contract that tenants have to keep the accommodation tidy. This is, however, a last resort and you should try to work things out with your roommate first.
If you are sick and tired of tidying up their stuff but don't want to look at it, buy a box to keep under the sink. Then simply put all their dirty dishes etc. in that box. It doesn't solve the problem in the long term but it's a great short term fix if you're having a busy day and haven't time to tidy for two. Make sure you let them know ahead of time if you are going to do this, and check that it is OK with them.
Avoid nagging - it annoys them just as much to be criticized for being dirty as it annoys you to have things dirty.
Consider having a time each week when you eat together for dinner, then clean the house. A relaxing meal together strengthens the good will between you and also serves as a cue to your roommate that it's time to clean now.
Distinguish between filth and mess. Dirty dishes left for months are unsanitary, but books and papers spread over the desk is just messy. Some people can't function or work in a non-messy space.
It is best not to hide people's stuff in an attempt to make them tidy. It usually simply results in heated arguments and not much getting done. For this reason, it is best you only ever start doing this if everything else has failed.
Cleaning up someone else's messy desk rarely works. Typically there's a system in place already, and moving stuff around usually results in items getting lost.