The larger the group in a meeting, the more valuable that time is. i.e. It's a productivity multiple of everyone in attendance, a tradeoff of being in the meeting against the work they could all be doing. So treat this high value time with respect and use it to express your clarified thoughts. If you are formulating thoughts as you speak, a smaller group, or a one-on-one would be a better use of time. If you have nothing to add, add nothing. Unclarified thoughts can lead our ant trail astray. Note: this is more about an attitude to other people's time, and a self-awareness, than a blanket rule for meetings.
Come from a default starting place of not-knowing, rather than a default of knowing. That is, taking a position in the form of: “I think we should make the text bigger, because (a) it's the most important thing to understand on this page, and (b) people will likely absorb the meaning of the text before the icon”. This is a tangible argument that others can build on top of, with agreement as well as disagreement: “I’d actually disagree with (a) since I think the call-to-action might be the most important thing on the page”. You can contrast that with statements in the form of: “This is wrong, the text should be bigger”. This portrays things in a categorical manner and shuts down potentially valuable intellectual debate.
The purpose of debate and discussion is to surface different viewpoints and arguments available for consideration. This is the bedrock of effective collaboration. But closing a discussion is important too, especially the open ended kind. A discussion is over when the available points of view in the group have been expressed and understood by all. So the capstone question for a discussion is: “has everyone been heard and have we all understood?”.