Every meeting should have a clearly defined mission statement ... I hesitate to recommend having an "agenda" and "agenda items" because the word agenda implies a giant, tedious bulleted list of things to cover.
Yet an agenda is the best tool for controlling meetings if the chair is any good. It says "this is what we will discuss and decide and only this". A meeting should not be a free-form discussion -- leave that for chance encounters in the office kitchen. It's a transactional form of communication, a tool to make efficiently make collective decisions.
Do your homework before the meeting.
Which is why agenda are circulated -- and even more because:
Make it optional.
Yes! And as Tom DeMarco points out in (I believe) The Deadline, meetings which don't stick to the agenda lead inevitably to everyone having to come to every single meeting just in case something gets decided. If the agenda is trustworthy, people will stay away who should stay away; only interested parties -- who will do the homework because it's relevant to them -- will turn up.
Summarize to-dos at the end of the meeting.
These are called "minutes". Properly written minutes are very useful and they don't have to be in legalese. The University Computer Club at the University of Western Australia, where I studied, have excellent minutes[1], written with a sense of humour.
Before I came to my senses, I used to be involved in student politics. And if that unpleasant experience taught me anything, it was the power of meeting mechanics. A well-run meeting is an extremely useful institution. Get in, discuss, decide, get out. Bam. No ambiguity, nothing left hanging.
As a chair there is one rule that counts: don't let the meeting get side-tracked. Stick to the agenda, work it. People quickly learn that they need to get their stuff onto the agenda in advance and the whole process begins to work better. Discussions become more focused, decisions can be made quickly and efficiently.
Those who are interested might like to join an organisation like Toastmasters or the Penguin Club to hone their skills, or get involved in committee work, or join a union, incorporated club or political branch. The skills of running an effective meeting are very useful. I applied them during my capstone unit at uni; my team delivered 92% of agreed functionality on-time with no significant defects. And part of that was running tight meetings.