Normally, I find Spring is usually my busy period.
It's a time where a window cleaner (or two) has given it up as a bad job sometime during the Winter and the months have passed and potential customers are desperate for their windows to be cleaned.
I've been lucky these past two years, since I've found areas that previous window cleaners used to dominate; yet have given up window cleaning.
I also had a good idea of their charging, so could charge reasonably more.
If things do go quiet for you, just focus on Spring and all those customers you'll get.
Remember, if it was an easy job with nice working conditions, everyone would be at it!