Experienced freelancers know that sales are never guaranteed, and that they come and go. However, that doesn't mean that the the time you spend not making sales is wasted, not if you use it wisely.
The short-short version of using the time wisely would be self-improvement. How? There are many things that you can do, and what you choose is solely up to you. Here are some suggestions (basically, things that I've tried and that worked for me):
1. Improve Your Skills
No matter how good you are, there's always room for improvement – plus, the better you become, the bigger the demand for your services will be. Go to a course related to your niche, learn from tutorials and books, watch what the experts are doing and think about how to apply it to your own work. Once you start selling again, your service will improve, meaning happy clients, recommendations, and the possibility to charge more.
2. Learn New Skills
Is there something you could add to your services, if only you were familiar with (insert another skill here)? Learn it! Maybe it's working with a new software, or learning another writing technique, or expanding into another niche. Whatever it is, use the idle time to learn it – the time will pass faster that way, and you will have more to offer.
Or, you could learn something completely new and unrelated to your current services, and offer that. With prices starting at $5, Fiverr is great for that kind of experiment – someone will try you out, and you will see whether it works for you or not.
3. Learn About Marketing
Whether your services are related to marketing or not, you need to advertise your business, and you need to know how to do it efficiently. Perhaps what you offer is awesome, but only a few people know about it? Advertising will take care of that. There are plenty of books, websites and tutorials on the topic, so find something that you're comfortable with, and use that knowledge.
4. Read for Pleasure
Quiet periods can also be great to relax a bit and recharge your batteries. Read books, watch movies, listen to music, take on some hobbies... Enjoy yourself! It will not only help you rest, it could also give you some new ideas, help you broaden your horizons, and give you a fresh perspective.
5. Play with Your Gigs
Can you improve your gig description and make it more clear? Can you make it more attractive? How about changing your title a bit, playing with keywords, maybe adding another extra? Adding a new photo, or an example of what you can do? If you're not getting sales anyway, it could be time for experimenting with your gigs, until you find something that works.
If you're offering a genuine, useful service, sooner or later, the sales will come – and in the meantime, you can work on yourself, take care of yourself, and have a good time doing it.