Your Flow Level is calculated from the average of your points over 3 months. Points are earned by completing the activities on your Score tab. Some activities earn more points than others.
Maintaining your Flow level
Since we average out your points over 3 months you need to keep your points up on a monthly basis. That means each and every month or your average score can go down and we don't want that.
To find out how to get to level 4 by completing the most valuable activities you need to check out this article. How to get to Flow level 4.