Some people have a strong sense of hygiene and regularity in life. Others are casual and do not take things at responsibility. However a basic sense of hygiene and cleanliness around the room is essential. Look around you and at other people who share rooms and judge if you are being a tad bit paranoid about keeping the room in shape. If your room mate is a busy person who is using the room as just somewhere to sleep and not 'live', their values might be different and you have to give them the space.
Maybe you are being a hygiene freak and your roommate might even hate you back for that. If you still think you are justified, then try finding some one who believes in the same principals as you. Choose a right person in the first place.
Try to make them realize indirectly:
This one may take time but is the most civilized of all tactics. Hint to your room mate that you like a clean place to live and hygiene standards. At times do everything yourself including the dirt dishes and laundry so that the other person is morally embarrassed and decides to help, seeing you work hard so well. You can keep a specific day for cleaning the whole place and tell the person excitedly about it.
Take the direct approach:
Talk it out gently, in a casual tone that her habits are disturbing you and you like a clean place to live. A genuine person will never want to make life uncomfortable for some one. It is very much possible that your roomie has no idea that her habits are disturbing to you.
If these things do not work or produce little results, get down to business. Make a chart and delegate responsibilities of cleaning the room, dishes etc. Put up a chart in the living room or on the refrigerator door. This way the person will be forced to do his/her part of the job and will know the reason of your sour face when he/she does not keep up. At least he/she will not wonder why you are being so cranky.
Separate the mutual areas:
If you share an apartment, keep your area like your bedroom clean and make the living room livable. Clean the parts of the place that you use. If sharing a room, it is going to be difficult. Keep your wardrobe, bed and study table clean and make sure your roommate knows he/she cant mess them up. In the laundry, keep a separate basket for his/her dirty clothes and do the same in the kitchen for his/her dishes. Perhaps at some golden moment she is going to realize how good and clean your portion looks and clean his/her own.
Get professional services:
If your roommate is too lazy or busy to work and clean, suggest to get professsional cleaning or a maid who will charge you both . This way either he/she will agree to pay or work himself/herself.