Look at your current property, identify what you use often and day-to-day and set these aside so you are easily able to seperate what you need to store.
If you don't use something or haven't used it in over 6 months, chances are you don't need it. Either throw it out or get it stored.
If you are planning on leaving a lot of goods behind at your old property and starting afresh when you reach your new home, considering donating your unwanted goods. One man's trash is another man's treasure.