I've already touched on this previously, but I feel it needs its own chapter.
DON'THAVE AUTHOR'S NOTES LONGER THAN THE ACTUAL CHAPTER!
I can't say it enough.
It is annoying and completely unnecessary.
A published book does not have any author’s notes and the readers get along just fine. If you need to explain things at the end, then go back and re-write the chapter. Obviously you have missed a few crucial points.
Absolutely avoid putting them in the middle of a chapter. It completely ruins the flow of a sentence, paragraph etc.
If you do chose to have a note at the beginning or end, it should be the engage the reader in some way e.g. a competition between readers relating specifically to the book.
This is about to get a little tangential, but bear with me (don't even get me started on people who say 'bare with me').
Do not beg for readers. Do not beg for comments. Do not have a hissy-fit about your personal life. Guess what - I don't care about the guy at school that won't notice you. I don't care about the fight you're having with your friend. As a reader I just want to see my otp get together and finally kiss.
Having said that, sometimes it is okay to mention your personal life. I have done it on numerous occasions to explain why an update was so late e.g. Sorry for the late update. I have school/work/university/exams/social life etc. In fact I often do this when every single comment I received on a chapter says 'update!'.
I don't withold updates to annoy you. I'm not being purposefully mean. I simply can't write and proof-read that fast. It takes time. If I am getting someone else to proof-read my book, then I need to give that other person time to check their email, proof the work and send it back to me. Then I have to get time to check my email, and post it up on various websites.
I post on up to six different websites. It takes me about half and hour to get one chapter posted on the different sites, because I have to upload the chapter, get the chapter titles sorted, type in tags, make sure it has copied across properly. Commenting with the word 'update' in it's various forms when I have given you a chapter an hour previously, really bugs me. If it has been a month and there is no update, fair enough, comment all you like about what a horrible author I am - but if you've just read the chapter, don't. Just don't.
Despite the fact that I have just completely bad-mouthed author's notes, they do have some good attributes. For websites where readers can post comments anonymously and ask you questions, it is a good place to answer them. Also, if you keep getting the same kinds of questions from readers, it is a good place to address it once and for all so that everyone can see the answer, and stop asking the same question for the millionth time.
They are a good place to get information from your readers, and engage them in some way. For example, I occasionally use them to ask if anyone is interested in proof-reading work, or working out translations for chapter titles. I can usually get a response out of someone in this way.
Finally, they are a good place to wish your readers a Merry Christmas, Happy Easter, Happy Hanukkah, Happy Valentine's Day, etc. If I am posting a chapter around the time of some kind of religious/social event, then I try to acknowledge it if I know about it (I don't know every type of holiday around the world, so sincere apologies for not acknowledging them all).
If anyone has any tips of there own to share, please do so in the comments. I am planning to only have one more chapter of hints and tips after this one, so get a wriggle on with those ideas!