The list may be way longer than you realize, including not only smartphones and computers, but also:
Whenever possible, try to turn some of these devices off when not in use to maximize available bandwidth. Consider having family members stagger their online schedules or work in “shifts,” for instance.
Similarly, try to alternate work and leisure time so that you're not trying to stream your favorite shows while someone else in the family is on a video conference. All of these media services tend to use high bandwidth, and so will impact the performance of other activities in the home:
In addition, it's helpful to turn those separate devices off when not in use (not just let them go into "sleep" mode).
Finally, limit your uploading and downloading of large files during the work/school day, and schedule cloud-based backups to happen overnight to free up daytime bandwidth.
It may take some planning and practice, but by following these guidelines, you can optimize your home connection and make it possible for everyone in your household to keep your lives running online.
Have you tried everything and are just not getting the performance you need? There are a couple of popular solutions you might consider: