If you are scheduled to have a video consultation a stable internet connection is essential.
If you are on WiFi, rebooting your router before the consultation can help considerably (simply turn off your router, wait 30 seconds and turn it back on).
If you use a VPN, please disable it as it can cause problems.
Limit usage of high bandwidth applications elsewhere on your network, e.g. Backups, YouTube, Netflix etc.
If you are planning on using your phone's data, a 4 (or even 3) bars phone signal on 3G or 4G is normally sufficient for a Video Consultation.