Good filing will help you find that illusive document.
Keep filing categories to a minimum. If you don't you will be in danger of not finding what you have filed for easy finding.
Too much paperwork If you are swamped with paperwork of the same category like, bank statements, credit card statements, mortgage papers. The best thing that you can use is concertina type file. It will allow you to divide up a single category into different sections. If you really have a mass of paperwork then you should consider a small filing cabinet.
Documents to keep Keep all paperwork relating to purchases. Especially guarantees, keep them until all items have been paid for and delivered. Make sure that you keep the guarantees until they have run out. Better still keep them for insurance purposes so you can prove ownership in the case of a claim.
Most financial papers relating to bank statements, loans, overdrafts, credit card statements, tax papers, solicitors letters etc can still be needed for up to 7 years. So hold onto them. After a year box them up and put them away in your loft or roof space.