As we all know we learn best from mistakes, but what if you don't know how to fix your mistakes.
About 3 years into my career I realize I did not make provision for the 'slow season'. As a matter of fact I did not expect it.
Panic was an understatement
While watching the paint dry, the clock tick and twiddling your thumbs you still have to find a way to be productive. Here's what worked for me (now I don't have slow days, I don't have slow seasons at all):
Identify reasons why customers are not consistent or not returning
Where can you improve with managing your time - eliminate or reduce customer wait times
Take a look at your scheduling system, make sure it's efficient, effective and convenient
Look at your environment from the eyes of the customer, make changes
Review your business policy (example here)
Clean up your service menu
If you sell products, you need an online store (PERIOD!).
If you are an educator, you need to allow your potential customers to view your classes and pay online. Increase your reach.
When you weather the slow season, it prepares you for the busy season.