Start by measuring what you have. Upload speed and latency matter more than download speed for video calls and screen sharing, so read the upload-speed guide and the latency observation before paying for a faster plan.
Then decide how much downtime you can tolerate. The connectivity budget guide helps you weigh a better primary line against a backup. A UPS keeps the modem and router running through short power cuts, and dual-WAN failover covers outages of the line itself. Read them in that order, because backup power is usually the simpler first step.