ICYMI, #10 through #6 are available here and here.
As promised, the last five are all content related and so a little more difficult to address than the technical errors.
#5—Not connecting the reader to your main character
It is vital that the opening connect the reader to the main character. This does not mean that the main character has to be likeable, but it does mean they have to be relatable. If there is no connection, the reader doesn’t care what happens to them, and will stop reading.
#4—Not planting curiosity seeds/giving the reader a reason to keep reading
Another way to make sure the reader does not want to keep reading is to write the opening so that there is nothing to be curious about. Try not to over explain. Give just enough context. Leave a question or two hanging for future resolution.
#3—Beginning the novel with backstory
Please, I am begging you, do not stuff backstory into the opening. It doesn’t go there. The reader does not need the backstory up front to understand what is happening if you are writing an interesting story. Backstory is like salt. You need just a little to bring out the character motivations, but too much makes the meal inedible or the book unreadable.
#2—the query and the pages don’t match
There are loads of workshops that teach people how to write great queries. Problem is, if the pages don’t match, it doesn’t matter how great the query is. Write a great novel to go with your great query.