I used to have a hard time speaking up in group settings — in meetings I'd have a point worth making and talk myself out of raising it, then watch someone else say the same thing ten minutes later.
What's helped is giving myself a simple rule: contribute at least one substantive comment or question in every meeting, early, before the anxiety builds. I also started volunteering to present project updates so speaking to the room became routine instead of exceptional.
It's still not my most natural setting, but my last manager specifically noted in my review that my meeting presence had improved — and now when I hold back, it's a choice rather than a default.