Use video. It helps people feel like they're all in the "same" meeting.
Use a headset. This will make your voice clearer and cut down on echoing.
Mute your mic. If you're in a large meeting, the organizer may mute your mic to cut down on background noise. If you're with a small group and you hear feedback, consider turning your mic off when you're not speaking.
Test first. If you have an opportunity to test your conference ahead of time, try it out to make sure your equipment works.