Cersei can be heard (in the trailer) saying that they have enemies in every direction and so the time has come to act sans any scruples. Well, from the finale of Season 6, it is clear that Cersei is still the badass person she was. The way she managed to bring all her enemies under one roof and ‘kill them all’, was a move nobody expected. For more of the Lannisters, stream Game of Thrones Season 7 online.

In the North, Jon is the new king (just like his half-brother Robb, sigh). With the help from Littlefinger and other loyal houses in the North, they are preparing their onslaught of King’s Landing and avenge everything wrong which the Lannisters have brought to them. *SPOILER ALERT* Though some Reddit users are suggesting that before that, a possible Stark reunion may take place (since almost every Stark is in the North).
Also Check : Game of Thrones Season 7 Spoilers

The White Walkers will bring down the Wall. That was expected when there are millions and millions of dead coming back to life. Since Jon is no longer a Watcher at the Wall, he will be saved. But other allies of his (at the Wall) will succumb to the attacks of the Walkers.
Euron wants to put an end to the Targaryen menace. In the TV series, he is not portrayed as he is in the books. As per the books, he is the most evil character in the entire A Song of Ice and Fire universe. Anyway, he wants to gain control over Westeros (which is very common, lol), with Daenerys by his side.

We might get to know more about Jon Snow’s parentage. In the previous season, it was clear that he is not Ned Stark’s illegitimate son, but his sister, Lyanna Stark’s son. So, we may expect some flashbacks (thanks to Bran) which will feature Rhaeghar Targaryen.
So, for more of Game of Thrones Season 7 action, stream it online. Valar Morghulis!