* take a look in the service announcements how did others make announcements (look especially for those starting with [ANN])
* make your ANN with as much info about the company as possible, presented nicely and easy to read (not a 2-liner, not a wall of text)
* stay available for questions, expect people questioning your business, especially at start; keep in mind that some will be nice, some may be harsher if they find mistakes or fishy or unclear things
Keep in mind that you, as newbie, won't be able to put images. If that's important for you, also consider acquiring copper membership.