Do's:
Do: create a free email to safely and secretly store and send information
Do: hide a self timing camera behind something if you are suspicious of someone
Do: use your pillowcase to hide things in
Do: use your gym locker to hide things in, not your regular one
Do: think outside the box. Think of what your parents would do is they were suspicious of you; where would they look to check for hiding spots? Do they have access to your letters or your diary? Those are probably the first places anyone would look if they wanted to see what you are up to.
Do: hide hints for passwords in pictures that you can post around your room. Just don't make them to obvious
Do: sew an extra pocket on the inside of you jacket.
Do: cut a square patch out of your carpet. But only cut on three sides so that it's like a flap. You can hide bad test grades, important papers, or memorabilia under there.
Don'ts
Don't: ever tell anyone what you are doing, no matter how tempting it is.
Don't: assume your parents won't look to see what you've been doing
Don't: ever use the "remember me" option when you log into something personal or secret
Don't: use the same password for everything
Don't: give away little hints to make your siblings or parents suspicious
Don't: write in a dairy or journal; use a password locked computer or a tape recorder instead
Don't: keep all you information on one disk or memory key; have a back-up ready of necessary
Don't: give your parents your friend's parents' numbers; use an alibi