The over-arching rule is: Don’t waste people’s time.
Don’t invite everyone in the known universe, unless they’re all genuinely needed on the phone at once. Talk to them individually if possible; it’s often more efficient.
If plans change and some people aren’t needed after all, let them know.
If you have people in different states/cities, use a service with a frecall 1800 number dialin, or at least a local 1300 dialin. People dialling in from home don’t want to incur a long distance bill just to sit on the phone for an hour to say their ten words.
Start the conference on time. If you intended to kick things off at 10 past, schedule the damn meeting for 10 past.