You start out by creating a complete profile where you highlight all your qualifications and talk about your expertise, and then you start participating in the community. The best place to start is by answering questions posted by students. You can also post projects, work on other people's projects and get paid for it, review others and get reviews for yourself.
Being active on Expert Connect means that you do not have to maintain multiple social media profiles and do not have to keep track of multiple channels. You can focus all your energy into one channel and gain maximum output.