What are some things you wish someone had told you about therapy before you started? I know some of these might be a given but I feel I got way to close to my therapist.

Mine are:
Don't get emotionally involved
At some point the therapist will leave in some way (move, change jobs, retire) so always be ready for it and don't get to close
Get your needs met by other people in your life
Advocate for yourself
Keep the boundaries firm and remember its a paid, professional relationship