The simplest way is to mechanically clean the casing. This is not recommended to use water and alcohol. About any solvent, too, to forget. If they get inside, instead of cosmetic repair you will need capital, and not the fact that it will end successfully. The maximum that can be done is to wipe the body wet, but not wet cotton swab.
Instead of a cotton swab is better to use a cloth designed for monitors or mobile phones. They are easy to scour the grease, paint and other stains on the body. In addition to mechanical cleaning, they completely kill germs.
In radioimaging also a special spray sold by Basf or "Editing" that is sprayed on the surface of the phone, and then erase non-woven cloth to avoid getting lint inside. Sure, disconnect the phone and remove the battery.
To rid the glass of the screen phonefrom scratches and you can use paste special. Before the procedure, make sure the top glass of your phoneand plexiglass, so as to clean clippaste only him. The paste is applied on the display and rubbed with a piece of suede or other thick fabric. If scratches appeared on the present glass, then get rid of them only replacing the glass.
Once again not to take risks, refer to the workshop repair the phones. There the dust can remove the special vacuum cleaner, purge, and removes dirt by using ultrasound. In addition you can change the erased keys on the new one.