For many writers, finishing a novel is an arduous process. For those who prevail, have a novel in hand, and decide to try to get it published, perfecting the query can be a drawn-out battle, each word and phrase under constant siege until only the strong remain. And then...then comes the *$!K#@G synopsis.
For those who have not experienced it, following is a simple 12-step process for writing that most nebulous, infuriating and vilified of all marketing products.
1. Realize you need to write a synopsis
2. Denial Part I - Ignore that realization
3. Start querying agents who don't require a synopsis
4. Feel good about yourself
5. Get a partial request from an agent, including the requirement for a synopsis (!)
6. Set aside a night to write your synopsis
7. When that night comes, cry vicious crocodile tears (place hyphen in the spot of your choosing)
8. Die a little inside
9. Denial Part II, aka "Screw this. I just won't respond to this agent's request" - moments later you will deny this denial
10. Discover there are exactly one hundred specific lengths a synopsis "must be"
11a. Spend weekend hammering out ninety-nine drafts of synopsis, each a different length
11b. Die a little more
12. Respond to agent request, and begin querying agents who require synopses between one and ninety-nine pages in length
And there you have it. Easy-peasy. Go forth and synopsize, good readers.
In all seriousness, I do recommend that you complete a synopsis prior to querying a novel. It is not what I'd call a "fun" activity, but it can reveal pacing issues or help you to distill your story into a query or one-line pitch. It's also a bloody slow process, one I don't recommend saving until you've had a request for one of these buggers.