What Star Trek Discovery is About – the Mission of the U.S.S. Discovery
I think it goes without saying that a starship named “Discovery” likely has a mission of exploration. “Discovery” and adventure are right in the name of the ship. Just like the Enterprise in previous Star Trek television shows, the USS Discovery’s mission is guaranteed to bring new villains, new heroes, and new worlds. It’s likely to be a scientific mission, not one of war, though there’s likely to be plenty of action.

Update (Jan 18, 2017): News that Sarek, Spock’s father, will have a role in Star Trek Discovery. This means it’s likely that the Vulcans will be a plot point in some form throughout the series. It’s unclear if Sarek will be in his role as Ambassador to the United Federation of Planets at this point in history.
Update (Dec 15, 2016): Given the recent casting announcement of three Klingons, it’s looking more likely that species will play a major role. Add to that Nicholas Meyer, who directed Star Trek 6: The Undiscovered Country, is a key writer for Star Trek Discovery. That movie focused around the Federation and the Klingon Empire reaching a peace agreement. The USS Discovery is likely involved in the early attempts at bridging the divide between the two galactic powers.