Advice: You don't know EVERYTHING about your characters

I've seen a lot of people writing stuff, excruciatingly painfully explaining every single twitch that character had in the first few pages of that story. People, we do not need to know the entire biography of someone right when you open the story. Why? Well, first of all, because we do not care. We are not yet attached to that character emotionally, so it's definitely not interesting. There are few authors that can pull this off, and they have their methods.
Best was to describe characters is, first of all, gradually, over the entire length of the story, so the reader gets to know it and gets attached to it, and then, use a lot of dialogue and interaction. You can very well describe your character through dialogue, he can answer inspired questions put by other characters, so you don't need to foolishly explain everything to your readers.
That should be a ground rule. Your readers are not stupid. If you hint them something, they will probably understand what you meant without trying to give them every single bit of information you have stacked up. Also, don't have every single character of your fully developed in your mind in the beginning. Of course, if that happens, it doesn't mean it's wrong, but you will be amazed at how much your character can evolve while you're writing your story. Every twist and turn in the plot, will obviously affect your characters, and through that you will find out how they're shaped and how they react to different impediments. Test yourself, put a character through a few different actions that would obviously endanger it. Write down how he or she would react to that. After doing that, you'll have a much clearer picture on how brave your character is. You can do this for a bunch of other qualities you can think of.
I hope my advice will help you, and hoping to see some feedback here.
Start writing.