Having attended thousands and thousands of meetings in my life, I do have an opinion on what makes for an effective meeting. This tip is about getting the agenda ahead of time.
I think that you can reduce the number of meetings that you attend by refusing to go to any meeting if you do not have the agenda at least two days before the meeting. It is hard to prepare for a meeting if you don’t know what is to be discussed. It is also possible that there is nothing on the agenda that interests you, so maybe you don’t need to go. Meeting planners who do not have an agenda a few days before the meeting do not appear to be well organized. Maybe there is no good reason for a meeting?