Writing for experienced users and first-time visitors is a key content challenge. A company tells an ongoing story to a consistent audience. If the company is doing interesting things and people are talking about its products, though, new people are regularly stopping by. These visitors are starting with little context, most likely just a link from an article or a friend.
Think about content like hospitality. If you're having people over to your house, there is a familiarity with those who've visited before. "Grab something from the fridge and relax on the porch. We have that drink you liked so much last time." Much goes unsaid.
For people who are stopping by for this first time, though, you go out of your way. "Let me show you around. The restroom is down the hall and to your left. Oh, that's Pixel. Don't worry, she doesn't bite."
Try to read your content, especially announcements, from the perspective of someone who hasn't heard of your company or product (or better, find someone like that to provide feedback before its published). The people who are already part of your story don't mind a short paragraph that bring visitors up to speed. Go out of your way to make everyone feel at home.