I've been editing a memoir/novel for a client. Some of the writing is really brilliant and some of the story is riveting but the book itself is flawed by inconsistencies, the kind of inconsistencies that many readers find annoying. Here are some of the things to watch out for in your own writing.
1. If you choose to use italics for blocks of text, make sure you use it consistently for the same kind of sections (e.g., flashbacks, dreams, interior monologues).
2. If you choose to use both third-person and first-person narration in a book, be sure that you use them for the same kinds of text and definitely don't switch from one to the other in the middle of a section.
3. Learn to use all punctuation clearly and consistently, especially if you are using a punctuation mark in a non-traditional way.
4. Avoid the use of "you" to address the reader.
5. Both past and present narrative tenses are useful and they can be used in the same writing but again, use them consistently. For example, you want to use present narrative for all full scenes and past narrative for summary.
Remember that you are writing for a reader. Readers are always looking for patterns. They want to organize your words and ideas and story in their heads. The more consistently you use things in a clear pattern, the happier the reader will be.