I'm here for over a month now, and I'm still feeling that other people are better than I could ever be. Don't let that hold you back! You'll miss out on discussions because you think you can't add anything, but the truth is, adding yourself to a discussion is something of it's own. I don't mean that you should start posting everywhere. If you stay yourself and are genuinely interested, your contribution will be interesting! I'll follow you.
I think everyone feels that way to some extent. That's probably why there are so many lurkers on the internet (not just here). Not speaking up out of fear of being wrong has led to airline crashes and patients getting the wrong leg amputated (as real world examples of why everyone should contribute). I think most people are on sites like this to hear what others have to say, and not just to give others their own opinions.