The trailers released thus far have offered a few hints as to how Prometheus ties into Alien. We've seen the egg room, and we know the Space Jockey will finally get her due. But more so than anything, it is one particular character that holds the key connection between the two films.
Warning: Major Spoiler!
It was Ridley Scott himself who has freely and willingly threw this new information out into the public about Prometheus, a film he is quite determined to keep a secret (for the most part anyway).
Though the Space Jockey is present in Prometheus, and does serves as a direct link to Alien, there is only one true throughline that, according to Scott, has been incorporated, and it rests solely with Guy Pearce's character.
Read the following statement from Ridley Scott to learn more.
The Prometheus is owned by an entrepreneur called Peter Weyland, and is played by Guy Pearce. That's the connection between the two films, and nothing more. Prometheus is a new film, a new world, and is full of new ideas. And of course new monsters as well."
Guy Pearce reportedly only has about a minute of screen time in the film, though it is clear that his character plays a huge part in the overall story arc of the entire franchise. Those fluent in Hungarian can read more:
Prometheus was released June 8th, 2012 and stars Noomi Rapace, Michael Fassbender, Charlize Theron, Idris Elba, Guy Pearce, Logan Marshall-Green, Sean Harris, Rafe Spall. The film is directed by Ridley Scott.