Many people do not realise the importance of looking after the documents for your vehicle. Having the service history for your vehicle can make a huge difference when it comes to selling the car, especially if it has been serviced regularly and by a main dealer.
Along with ensuring that you have the service book and that it is stamped every time you have a service done you should also try and keep receipts for other work you may have had done such as new brake pads or discs.
If you have lost the service book for your car then you can often buy a replacement from the main dealer or online but it will then be up to you to track down all the garages that have services the car and ask them to stamp the new book again so you have an up to date service book. If the car was serviced at a main dealer every time then you may be able to obtain a print out from the manufacturer to show when and where it was serviced which you can attach inside the book.
If you have brought a second hand car, you can also contact a garage that you know serviced it and ask for them to stamp a new book so that when you come to sell it you have the information already completed.