The best advice I ever got from a mentor was "Before you open your mouth, ask yourself: does anyone in this room need to know that I know that?"
It's a difficult question to ask yourself. Listen to other folks and wonder if they're sharing from passion, from need or simply to show they thought of the same idea/concept/angle and don't want to be seen as left out.
I try to ask myself "Who really needs to know this?" "Why do I need to share this?" "What happens if I don't say anything on this topic?" Sometimes I even sit in meetings with my hand over my mouth.
It is ok to speak up for any of the reasons above - as long as it is by choice and not by habit of chiming in.
Keep in mind....Part listening skills, part personal brand, staying silent can be a powerful choice.