If your looking to part exchange your existing car you will want to get the very best price. How your car looks will have a huge bearing on that price. You don't need to have your car professionally valeted as most car dealers will be able to see the potential of your car but you need to make sure its been recently washed and vacuumed and to a reasonable standard. If you have had your car regularly serviced just check and make sure that the service book has been stamped for each occasion that you had a service. If the servicing garage has missed a stamp or two get the service book brought up to date as this can make a huge difference on the amount offered. If a car dealership can sell your car on their forecourt and they don't need to send it to auction you will be able to negotiate a better deal too.