Most individuals manage their accounts reactively. Many people often start compiling them sometime in January, usually the last Sunday, when they need to be submitted by 31st.
If you want to grow your business, increase your profit (i.e. make more money for doing less work), or minimise your tax bill, then it is important that you adopt a proactive approach.
The tax year ends on 5th April with your self-assessment return due the following 31st January. So, if you only start looking at your accounts after the end of the financial year, then you have already missed your opportunity to take action and you are largely stuck recording what has happened.