A writer's style is the particular way that a writer uses words and language to express their ideas. Authors tend to have a very distinct style to their writing. For example, the poet Emily Dickinson uses a lot of dashes, unusual capitalization, dense quatrains and slant rhymes. You can almost tell a poem is hers just by looking at its style-how it is written, and with what techniques. Henry James, an American writer, uses very long, long sentences that are full of flowery descriptions and detailed commentary. Ernest Hemingway often wrote short stories that were stark and dry, with little emotional or narrative content. So, each author writes in their own unique way.
Imagery is a technique that can be used quite a bit by an author to make their writing seem more active, alive, and descriptive. Imagery is when the writer includes descriptions using the five senses-taste, touch, sound, sight and smell. So, for example, instead of saying, "Autumn was here," the author might describe autumn through the five senses: the smell of fireplaces, crackling logs from a bonfire, the crunching of dry leaves under your feet, the misty fogs of a cold night, the hazy moon and brilliant colors of leaves on the trees. Describing autumn using imagery, or the five senses, makes the reader feel like they are actually there, tasting, touching, hearing, seeing and smelling the scene that the author is describing. It is a great technique to have in your style, if you want to bring the reader right to the scene you are describing. On the other hand if you want the reader to be more imaginative and more in charge of creating the scene themselves and adding their own perceptions to it, leaving imagery to a minimum is another technique that you could use.
I hope that those thoughts help a bit; good luck!