The peak of summer and the peak of winter are when most people are focusing on their holidays and the work slows down. It doesn't have to be a time to sit there twiddling your thumbs, there is always plenty to do.
Here are some ideas to keep you and your team engaged during the slow down.
Bring work forward
Is there anything in your schedule for later in the week or next week that can get started now? If not, don't worry there's plenty more things to try, but project managers will love being able to bring work forward if they can.
Prepare for your next project
If you have a project scheduled but can't start it yet, consider preparing for it. Code up a demo of some cool loading or block animations you can bring to the kick off meeting. Catch up with the project team and see where the project is at and (if welcomed) chip in with some suggested improvements.
Work through your team tasks
I previously discussed the idea of creating a Trello board (or task list) of things your team can improve. Want to try out a new technology or way of doing things? Add it to your team task lists and work through them when you have some down time.
Write an article
If you work for an agency, chances are they have their own website with a blog to make themselves look like experts in the field. Why not take advantage of this and start writing articles based on your experience? If you're a designer, write about how colours subconsciously affect user decisions. If you're a UI developer, write about how important accessibility is. If you're a backend developer, write about automated testing and how it improves the end product. They also say teaching is the best way to learn, so start by sharing your knowledge.
Level up your skills
Join an online corse to level up in your field. You have the time, use it wisely.
There are plenty of things to do when you have some downtime, so why not try one of the above. Let me know if you do something that's not on the list.