This is the dirty little secret of novel writing--
When you come to the close of a WIP, it's time to start about writing a query for it.
No one - ever - just reads a manuscript because you write one. The act of putting all those words on paper means nothing. It doesn't mean you can write. It doesn't mean it's a real book. It doesn't mean anyone has to read it.
In the space 250-300 words, in a business letter, you have to convince them that they WANT to read it by being such a GREAT writer that they WANT your words on paper to become a book, sell it and hopefully make you both very successful.
And those 250-300 words are TORTURE. You think it's hard to write a book? Try condensing that book into two short paragraphs without losing the voice or the plot or a single element that makes it unique. Leave no question as to what the book's about, but make sure you don't give it all away. Pique the reader's interest so they want more.
Keep it simple. Focus on your main character and your main plot. Lead MC through MP and keep him/her active. If he's funny, make the reader laugh and never tell them he's funny. If she's nervous, make her twitch, but don't point it out by calling her nervous. If it's a "heartwarming tale", then query better not leave the reader cold.
Try writing a query for a book in print - one you're familiar with. (It's easier than doing your own and gives you an excuse to stall while feeling productive.) Once you have something that resembles Spark Notes of the Cliff's Notes of the Abridged version, you're good to try it on your own story.
Then the real nightmare starts -- summaries.