You should of course check with your installer before doing these things just to be sure that is his preferred method. It is better to ask these things up front than to find out later that is not the best way of doing things in your area.
Next, it is a good idea to get inside the pool and remove the liner. Do not take the pool apart. Just use a razor blade and cut the liner out a few inches down from the top rail. To make removing a large liner from a pool easier it may be necessary to cut the liner into thirds or fourths. Once the liner has been removed you can check the pool base and side walls. If you have a sand base with some sink holes a couple of bags of play sand from a nearby hardware store will usually be enough to level them out. If the bottom of the pool is full of tree roots they should be removed. If doing this messes up your pool base you may need some more sand to smooth it out. If there are grass and weeds present pull them and treat the area with a grass and weed killer. You should also check the pool wall very closely for any signs of rust. Rust spots should be sanded and painted.
If you have an overlap liner it is secured to the sidewall with coping strips. These plastic strips are then covered with the metal stabilizing rods. There is usually enough of the coping below the rods to allow for an examination, without taking any of the pool apart. The coping should be pliable. If it is old and brittle it will fall apart as you pull on it. If in doubt have new coping on hand, what you do not use can always be returned.A rule of thumb about gaskets. Rubber gaskets are usually reusable, anything else should probably be replaced. If you are in doubt have new ones on hand.
This is an important checklist if you are installing the new liner yourself. If you hired me to install the new liner for you, and I found all these things done when I arrived, don't be surprised if I give you a big hug.
Learn more about vinyl liners here.
AGP Pool Help - Everything on this site about Above Ground Pools