You can start by participating into the specialties community, answering a question is a good start point, where on every vote up on your answer, you are going to have more ranking points into your specialties.
You can always check where you stand by accessing "My Rank" http://www.bayt.com/en/my-specialties-rank/
More details on what you can do to get ranked can be obtained from here http://www.bayt.com/en/why-get-a-specialty-rank/
