Before you start thinking about preparing your will you need to know for sure what property, money and assets you wholly own. What do you have that is yours to give away, and how much do you owe to others? What exactly does your estate consist of?
If you have assets that are in joint names (or are legally shared with third parties) then these parts of your estate are more likely to automatically pass to the people you share the asset with when you die. In most cases this will happen regardless of what has been stated in your will.