To free mind from clutter, transfer what is in your mind to another, more physical medium. It can be paper or computer. This act of transferring is done by writing.
By writing on a physical medium our thoughts, we are free up space in our mind. By writing down our thoughts, we can more easily organize our thinking. Writing makes possible complex thoughts possible.
Use a diary, either paper or electronic, to write down your personal thoughts. Use a planner to for your activities. Pick what suits you. Some use one type of material to write down everything and others use different materials for different areas in their life. What you use to pen down your thoughts are not as important as having easy access to them when you need.
Try this simple technique and liberate yourself.