Speaking in a group conversation can be intimidating and depending on the organization you work in or the expectations of your job there maybe nothing wrong with being quiet, it may be a liability to your career. It can even matter in social situations that come up at work. Generally, speaking there is nothing wrong with being quiet, but if you want to assert yourself more in conversations here are some ideas.
First, give yourself permission to be silent. Otherwise it can become a self-fulfilling prophecy in which you never speak because of the feedback loop of pressure and anxiety you create for yourself.
You can try talking more often than it feels like you should. Even if this is a simple affirmation of what someone else has said. If you speak more often than you feel is necessary as a quiet person you are probably chiming in about the average amount. If you don’t force yourself to participate every so often you almost certainly will default to your normal amount of speaking.
While this may seem in opposition to the first point it important not deride yourself but at the same time encourage yourself. Don’t stress yourself out. Do your best to find a happy medium.
If it is work meetings you are concerned about make sure to be prepared, have some talking points written down ahead of time. If the conversation takes a unanticipated turn towards an unscheduled topic do your best to improvise.
Remember also that if the goal is to be heard and make yourself more present small contributions are better than nothing. Try accenting other people’s larger ideas with small thoughts. If someone is making an argument for or against a certain action or direction the organization might take fill in the gaps with little thoughts.
If you aren’t speaking remember to at least be honestly engaged in the conversation. Look the current speaker in the eye. Don’t appear too relaxed, sit up with a good posture. Take notes by hand even if you don’t need them. Be the person in the room who isn’t distracted by their cell phone.