ideas?

hi i'm ding a movie about sci fi but i'm not that good a writer any sugestions ive thought of a few possible plots

star trek first contact type thing where the ship is taken over

trying to stop pepole from destroying the world a very basic plot but it would lead up to a big final battle

Why not try having a sci fi weekend and rent all of the1960's and 1970's B-type sci fi movies you can. You might be inspired by some sub-plot(s) and be able to make your own movie loosely based on the idea. I'm not suggesting remaking or copying a film, just looking for undeveloped sub-plots that you might be able to build on.