Once you get to Settings, click the Video tab on the left-hand side, and uncheck the box that says Enable HD.

When you do screen share, only share as long as absolutely necessary

Be sure to stop screen sharing when you no longer need to show your screen. Also, avoid asking students to screen-share.

Use online collaborative documents rather than screen sharing

Services like the G-Suite let multiple people open and edit a file simultaneously. These services use less data than streaming video, while still allowing everyone to see changes as they happen. 

Mute your audio when not speaking

You can also reduce your bandwidth further by muting your audio when you're not speaking. This is true for students and teachers. Use the Mute button in the bottom left corner of the Zoom screen to toggle your audio off and on.

If the connection is really poor, you might also consider using a phone call to connect to a Zoom meeting instead of using computer audio within the meeting. The phone numbers to connect to a Zoom session are usually included in the invitation you generate, and can be found under the heading "Dial by your location."

Consider foregoing the recording option for now

Teachers often record their classroom meetings. Zoom meeting recordings will take up significant bandwidth so perhaps you can skip recording your class sessions if you're having difficult connecting. 

Improving your Zoom performance overall

Limit high-bandwidth activities by others at your location. This isn't always possible in, say, a hotel, but if you're staying in a location where you can manage it, know that other people using the Internet will affect the bandwidth available to your Zoom session. If you can, please consider asking others to avoid streaming video or music, playing online games, and similar activities, as all of these activities can noticeably impact your Zoom performance. Someone watching Netflix in the other room? Politely ask them to read a book instead.