I don't believe in "slow" seasons. I don't think they exist.
By most people's standards of a "slow season," I am in one now. Being in the niche I am, winter is not my peak season. But I also don't feel as though I am in a lull. I am spending this time doing everything I won't have time for in a couple of months. I have applied for a volunteer teaching position. I have re-organized my follow-up schedule for the next couple of months. I have registered for networking events all the way into the next quarter. I have researched and reached out to companies I have a strong desire to work with in the future. I have confirmed my priorities, on paper and in my head. I have re-connected with friends and family. I have stopped neglecting my own social media, which often happens as client accounts take priority over my time. I have taken on some web design jobs, something I don't often have time for but is a great change of pace creatively and technically. I have started writing an e-book, that's been in my plans for 2 years. I have been brainstorming events I might like to host later in the year.
Experiment. Prioritize. Get prepared. Get Ahead. Grow.
Productivity is not defined only by the monetary value of your work. It is defined by relationships. It is defined by the steps you take towards your goals. We don't just need time to work for our businesses, but also on our businesses and ourselves... When you find yourself in a "slow season" use it - Experiment. Prioritize. Get prepared. Get Ahead. Grow. Re-connect with your network, and tell them what kind of support you'll need later on.