Clean your pool
The first thing that you must do is to make sure that clean all the leaves, debris, insects and dirt. You need to make use of your pool vacuum or just do the cleaning using a net. It is also important to make sure that you clean put the pump basket and the skimmer.
Balance the water chemistry
It is advisable that you balance the water chemistry in order to protect your pool from scale buildup or corrosion. You can do this by use of a small water test kit whereby you adjust the water to the right levels of pH, total alkalinity and chlorination.
In case you would like to add winterization chemical kit, you can also do it. These kits have the ability to put high levels of algaecide and chlorine in the water in order to prepare it the coming winter months. There are ready made kits that you can buy and make sure that you use them according to direction provided.
Be good to your heater and pump
You need to disconnect your filter and pump. You have to ensure that all water is fully drained from the pool pump. For insurance, you need to turn it upside down and make sure that you dump any extra water out. You should also remove the drain plugs from it; there may be one or two of them that can trap water inside. After you have drained the pump you should then turn it on for a few seconds to allow any remaining water to be expelled from the impeller. Store any parts or small plugs in the pump basket, so that you find it easily the following year.
In case you have a heater, drain it and ensure no standing water is left inside. Make sure you blow the water out using a shop vac or compressor. Drain the heater fully, remove all drain plugs and stash them in the pump basket for use in the next winter season.
Ensure no water in the pipes
Loosen and unscrew any quick disconnect unions or fittings at your filter system and pump. From there, you should then make sure that you blow out the pool pipes. You can use an air compressor or wet dry shop vacuum. Force all the air from your pump down the skimmer and through the suction pipes.
Clean the filter
You need to remove the filter hoses and spray the cartridge filter elements using filter cleaner. You should then rinse them using a garden hose. One caution you should observe is avoiding use of acid wash at pool closing time. Ensure you open the drain at the bottom of the filter to allow the water move out in the filter outlet. Make sure that you open up the air relief valve in top in case you have it.
If you cannot do the work by yourself, it is advisable to hire a professional to help you in the process.