Micro Fiction — Up to 100 words. Very difficult to write, but an interesting exercise for you to try. Like all stories, this needs a beginning, middle, and end.
Flash Fiction — 100 to 1000 words. A bit easier to write, since you can go into more detail and dialogue.
Short Story — 1000 to 7500 words. You should be familiar with this form of writing from English class in school. Write a short story as an assignment on such and such theme.
Novelette — 7500 to 20,000 words. Something like this could be expanded into a novel.
Novella — 20,000 to 50,000 words.
Novel — 50,000 to 100,000. Accepted lengths in today’s publishing market. On average around 80,000 words.
Epics and Sequels — 100,000 plus.
What about word count for various genres?
Fantasy Genre — 80,000 and 150,000 words
Romance Genre — 80,000 and 100,000 words..
Historical Fiction Genre — 85,000 to 100,000 words.
Mystery Genre — Stand-alone mysteries 75,000 and 100,000 words. Cozy mysteries 50,000 to 60,000 words.
Suspense/Thriller Genre — 90,000 to 100,000 words.
Speculative Genre — 80,000 and 100,000 words.
Young Adult (YA) Genre — 40,000 and 75,000 words. This depends on the target age group
Western Genre — 45,000 to 75,000 words.
If you plan on submitting your completed and edited work to a publisher, make sure you check their website for the exact information on the word count they accept. If you are going the self-publishing route, you have a more leeway. However, you should take into consideration how many self-published books are vying for readers’ attention. Being a writer and — I hope — a reader; check out various eBooks to find out their word count for the genre you want to write in.
You can start out by writing short pieces before tackling something like a novel or an epic novel. Create a few collections of short stories in the genres you like. As a self-publisher this would give you a presence in the writing world while you work on a novel.
Write flash fiction and post it on your blog, will give people something to read and let them see what you can do. This is a way to start a following for when you publish your novel or collection of short stories.