Many writers use writing groups or book clubs to help them to improve. To review others' works, or to let other readers and writers know how to give you constructive advice on your own, consider typing up a list of questions.
Here are some of the basic questions I have used in my own writer's club.
1. Description or Blurb - Clarity, conciseness, consistent voice, level of tone / diction / syntax, grammar, intrigue, clear genre and age level.
2. Opening - Lines & paragraphs have s spark or a hook?
3. First Chapter - Is it confusing or vague through the first chapter? Does it draw attention? What can be done to improve it? Are things defined well enough for readers who are not familiar with the world or topic?
4. Draw - Does the first chapter(s) end where I am drawn to turn the page?
5. Dramatic Questions - Are the dramatic questions obvious?
6. Inciting Incident - Is the inciting incident obvious?
7. Original World / Actions - Are the original world and original default actions clear?
8. Realistic - Are the details consistent and realistic, or a little bit...strange? Unfathomable? Why? How can that be fixed?
9. Repetition - Are there any words or ideas that are repeated several times, or which are weird in the descriptions? Which should be removed?
10. Flow - Does it flow flawlessly and smoothly instead of bumbling with run-on sentences or awkward things that make reading difficult?
11. Grammar / Punctuation - How well is the grammar and punctuation tackled?
12. Tense and POV Consistency - Does the tense or POV change, or is it flowing and consistent?
13. First Person - Is the word "I" repeated over and over in this POV?
14. Voice (etc) - How well is voice conveyed? Tone? Diction? Syntax?
15. Descriptions - How well executed are descriptions for sensory / thought / emotion / picture? Do the descriptions ever slow the progress of the plot in favor of pretty phrases? Do the chapters use long passages of exposition to fill the reader in on histories and back information rather than let the story itself hint throughout the entire work what has happened before? Are there moments where you begin to skim through rather than read diligently? Beware. Are there symbols or metaphors relating to a bigger picture or theme wrought throughout the descriptions? Is there too much dialogue? Too few dramatic questions hidden in the descriptions? Are the interactions between the characters riddled with enough tension or micro tension that the environment itself, as perceived by a character, has become a character in and of itself?
16. Plot Clarity - How clear is the plot? Does it lag?
17. Recommendation - How highly would you recommend it to others based on a scale of 1-5? Would you buy this book, even from first glance?
18. Overall Judgement and Flavor - Personal opinions. Ideas on how to improve, or where.
19. Minor Opinions Per Chapter - Comment on what you liked or didn't like per chapter. Or other information.
In your own writing, make sure you pay very special attention to your opening line / paragraphs / first chapter. It can make or break your book, when readers are concerned. Think of ways to shorten what you are saying in order to make it more concise, quicker in pace, and faster to reveal what is going on. Never dally or dance on pretty wording, unless you break the rule intentionally for odd characters' strange dialogue, or other similar exemptions, but do make sure it is snipped quickly. My first rule to writing your best is to hook, line, and sink. (Set up, punch the gut, and drag them into the next book kicking and screaming.)