Today, I just wanted to give a few quick tips on writing a good summary.
A. Figure out the main tension of your book. What does the main character want? What does the antagonist want - or what might stop the main character from reaching their goal? Once you have figured out what you want your readers rooting for - and what you want them fearing more than anything - you've figured out your tension point. And that's what is going to make your summary interesting.
B. Talk about main characters. Don't explain every single secondary character. I've got a family with six children in my books. I'm not going to be writing about every single one of their children in my plot summaries. Normally only one gets mentioned, and she's the one who becomes a vital sidekick to the main character. Don't waste time trying to explain who's related to who and what so-and-so is doing while the main character is fighting for their life in another room.
C. Talk about the main plot. The sub plots are interesting and could be fantastic to explore if a literary agent or publisher asks you for a more detailed summary. But for now, stick to the main plot. Remember what the main character wants and what is stopping them from getting there. Explore that.
D. Skip scenes and even chapters. You might think everything in your book is interesting - it may well be! - but you simply don't have time to explain every single death, revolution, or ship sinking that occurs in your novel. Skip to the really important stuff - the stuff that impacts the main tension point in the most relevant and easily traceable manner.
Lastly, it's probably wise to write your summary in one sitting, while your head is in the game. Then come back and edit later. Make it attractive. It's probably not wise to start with a lengthy explanation of setting and characters' histories. Start with the main tension. Your first few sentences are very important. An agent or publisher will probably see your summary before they see anything of your book. While you may feel summary writing is the worst work you've ever done, it pays to polish it. You never know when it might make all the difference.