1. Don't post meeting links on social media or public platforms if it can be avoided. You never know who might join the meeting.
2. Make it mandatory that people join the meeting with a password.
3. To prevent other people from sharing inappropriate images during a meeting, click on the arrow next to Share Screen and go to Advanced Sharing Options.
Then select Only Host so that only the host can share his/her screen.
4. To prevent unwanted visitors from making inappropriate comments, go to Manage Participants. Mute EVERYONE. This is also helpful in large meetings when people forget to mute themselves. Then you can decide if you want to allow people to unmute themselves to speak to the group or not. If everyone is muted, they may need to raise their hand to share.
5. Zoom lists other precautions such as using the Waiting Room, Lock Meeting and Disable Private Chat features HERE.
I'm sure other people will have more to share on this topic as well as more advanced advice.