@Shamidock (sorry this is so long) The plot really depends on the type of story you want to write. For example, with imagines I find it easier to follow the plot or certain scenes of the movies/TV shows as a guide, and alter it as I find convenient. For an independent story, I would say to go along with the usual exposition, rising action, climax, falling action, and resolution. That way, you would introduce the characters and their world, and then build the action, etc.
I can't really help with descriptive writing. I find it hard to come up with good adjectives, but I definitely recommend using a thesaurus. Thesaurus.com is a great source for that imo. But I guess what I recommend is, try to challenge yourself and come up with complicated ways of saying simple things. For example, instead of saying "He saw her running away" say "He sharply turned his head when he felt a sudden rush of wind blow past him. He realized it was his girlfriend, escaping from a danger he hadn't yet identified."
I hope that was of any help! If you have any other questions, or if you would like me to clarify something, let me know! :)