One thing that this trailer does excellently is build tension slowly. The first twenty seconds of the trailer are relatively silent, until the background music of vocal chanting begins. The viewer hears a few short "HA" chants after brief clips, after which it begins a slow, intimidating rhythm of chanting. As the trailer goes on, the music builds, with drums and more voices coming in to increase the intimidation factor.The music stops to allow a character to deliver a dramatic line, but then increases even more with the intensity.
While people who don't watch the series won't understand why these things in the trailer are happening, the trailer does try to gain their attention by focusing on what is happening. The trailer shows a great deal of fighting, intimidating dialogue, and a bit of sex appeal as well, which is a bit shallow, but it shows that they know how to get people's attention with the trailer.
If there's one thing this trailer could do better, however, it would be that it could emphasize more of the political dialogue aspect of the show. Game of Thrones is, in reality, a very rich and well-written show, for the most part, and this trailer doesn't really reflect that. It seems mainly focused on appealing to fanservice and the audience's sense of "ooh, that looks cool," and that's not necessarily a bad thing, especially considering how well it manages to avoid spoilers, but it could focus a bit more on the deeper, more personal aspects of the show that make it really worth watching.