Wideangle shots are used to show setting and add to the visual spectacle of sequences
Ridley Scott (director) filmed in a slow frame rate to give the models the effect of movement/motion
Some scenes in Alien were shot using a handheld camera helping to give a sense of realism and immediacy (such as close-up scenes in corridors).
Also helps to create a claustrophobic effect, as if the audience are right there in the scene.
Over-the-shoulder shots are also used: in the scene in which Parker dies, it's shot so it feels like we're with Parker fighting the Alien, and seeing what he's seeing.
Sometimes, highangle shots are used; they create a sense of scale as to how big the Alien is in comparison to the crew