If you’re interested in writing science fiction, fantasy, and/or horror, I heartily recommend attending a few conventions. Conventions vary widely in emphases and in “personality”, so a particular convention may not be a good fit for your tastes. For example, some are more devoted to media (e.g. TV, movies and comic books) rather than prose fiction. Nevertheless, many conventions bring together readers, writers, editors and other people involved with the sf/f/h written word. They can be fun and very informative.
If you’re just starting out as a writer, going to a convention can really open your eyes to various aspects of writing and publishing. You can often sit down for coffee with professionals and pick their brains on any (relevant) subject. You can also listen to panels where professionals talk about how they do what they do.
You can find a partial list of conventions at Locus magazine, but there are numerous conventions not on the list. To find out about conventions in your area, just go to your favorite search engine (e.g. Google) and search for “science fiction convention city” (where city is the closest city to where you live).