Summarize this article in one sentence.
A wired connection is usually more reliable than a wireless connection.  If PlayStation Now fails to stream or connect properly through a wireless connection, try switching to a wired connection. Sony recommends using a wired connection with an Ethernet cable for the best results when using PlayStation Now. If your connection is poor when using PlayStation Now, you may be using too much bandwidth. Make sure that there aren't any large downloads or streaming services (such as Netflix, or YouTube) running on any other devices connected to your wireless network.  Large downloads and streaming services running on smartphones and other computers can interfere with the streaming speed for Playstation Now on your PS4.

Summary:
Switch to using a wired connection. Suspend or cancel any large downloads and other streaming services.