What a lovely question! It's nice to see people wanting to get more involved in this wonderful community.
As others have said, you don't have to give any advice that you're not comfortable with giving. Stick to general points to start with, or just offer encouragement to newbies, and as you gain confidence you'll find yourself adding to what you say to them.
Some of us find we have specific "roles" that we tend to broadly stick to - so you could just respond to people on the Welcome forum, for example, which is a good place to start. I'm in the UK and there aren't a lot of us here, so I tend to post mostly in response to UKers because I feel I have more to offer in terms of suggesting foods, for example, and newbies can be confused by the more common use of American bg numbers as opposed to the rest of the world. A few years ago I posted mainly on the Grief forum because I was having a hard time myself and it helped me as well as others to feel that I could speak from the heart.
So I would say - just post wherever you feel you have something to say. It could be as simple as agreeing with others who have posted in a thread, consolidating a point they have made, or maybe adding a short comment to bump the thread up if it's getting lost down the list.
You'll be fine!