I'd written for years before deciding to seriously pursue publication. Once I started on that path, I realized there were a lot of things I didn't know or didn't know how to do correctly such as point of view, proper manuscript format, and more.
When I decided to submit my story to editors and agents for the first time, I was told I needed a synopsis in at least 2 forms - one ranging from a single sentence to a couple of paragraphs to include in my query letter. The second form was a longer version to submit to an agent/editor upon request along with the first 3 chapters. The general rule of thumb for a synopsis is to summarize the highlights of the story into 4 to 5 pages. My first attempt at a synopsis was 24 pages long. And I felt I'd only included the "important stuff." Luckily, I met a few great women who were more than willing to share their wisdom and their time.
If you live in an area that doesn't have a writing group close enough to join (like me), there are some great places on the web that can teach you what you need to know. One of the best places that I've come across is Janice Hardy's Fiction University - Fiction University Ms. Hardy has posts on nearly every aspect of writing as well as posts on how to query agents/editors and editing after that 1st draft is finally finished. She also has a section on the writing life. Just one word of caution, make sure you have a few hours to spend online. Once you get started reading all the great articles posted, you'll lose track of time pretty easily.