Unfortunately, readers will be trying to figure out your secrets the whole time and, as we've said before, they are super geniuses. Their reaction is directly related to the amount of time between when they figure out your mystery and when you reveal it.
Obviously, you want them to figure it out as late as possible (zero words; though a smug nod is okay too; it means the reader thinks they figured it out before "most people," which makes them feel good about themselves).
You should know this is very hard to do without trial and error, which is why God created beta readers. A good beta reader can help you figure out which secrets are working, which are not yet, and which are so annoying because oh my gosh it's so obvious HE'S YOUR LONG LOST TWIN BROTHER, YOU TWIT!!
When you find readers are picking up on a secret much too early, there are at least two things you can do.
1. Be more subtle. Figure out what the reader picked up on and remove it. (Be careful, though. If you withhold too much information, the reader will feel tricked. If that chart went into the negatives, this is what would go there.)
2. Add misdirection. Make the reader think they know what's going on, even though it isn't. Scooby-Doo was a master of this . . . for 7-year-olds. If your audience is any older, you'll have to get more creative. The trick, I think, is to believe your own lie as you write it.
I think I'll talk more about misdirection later. For now, do you guys have any other ideas for successfully hiding a secret from the reader?