There are a lot of good points about a strategy for speaking up in meetings, but I think it is simpler than that.
We don't have apps on our phone that will tell us if our comments will be successful and well received (yet!), so it's only reasonable to expect for all of us, some of our comments won't always be the insightful, problem solving, brilliant messages we want them to be.
Don't over think it. That's so easy to do when deliberating whether or not to speak up. Ask yourself this: Are you making a comment that you believe can solve the problem? Is it in the best interest of the company or your product/area? If so, say it. If your intent is good, you NEED to contribute to the conversation.
People at times put too much stock in who they think the experts are in the room, or want to wait until senior leaders speak first.
I wish I had more confidence earlier in my career, because the reality is your company needs your input, and you can't over think this. If you feel like your comment can contribute to success, use common sense about your delivery and say it. You'll be much better off in the long run, and your coworkers will appreciate every perspective, even if they ultimately don't agree.
In many organizations, our leadership readiness is measured in part by our willingness to speak up in meetings. How we speak off the cuff can have a bigger impact on our career trajectory than our presentations or speeches, because every single day we have an opportunity to make an impact.