Ideally, if someone will be participating by telephone or videoconference, assign one person at each location to establish the connection a few minutes before the meeting is scheduled to start, so everybody doesn't sit around waiting while technical difficulties are worked out. Test whether people at each location can see the pictures or whatever they're supposed to see; and then leave the connections turned on while waiting for the meeting to start so you're not left saying "It was working a few minutes ago".
If I have a lot of stuff to say, sometimes I'll send an email shortly before the meeting (preferably long enough before that people might have time to read it) and then at the meeting I'll just briefly mention the email, hopefully motivating people to read it if they hadn't already.
I don't mind if meetings ramble somewhat; that can be productive. But if I feel it's getting into conversations that could more usefully be carried out among a subset of the people present, and if I'm not the chairperson, I might just ask "Are we following the agenda?" or something to get people back on track.
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