TIPS:

1. Sharing overlap:
Beware, many games place your saves in a common folder. If you use Family Sharing between accounts on the same computer, your saves for certain games might be shared. Users have reported that an account sharing its library will also share its Steam Cloud (this affects both shared and separate computers).

2. Simultaneous library use:
Family Sharing normally only allows one user to use an account's library at a time. Two users cannot play different games under one account's library. However, you can work around this restriction by running Steam in offline mode on either account.

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1. Join this group with the account you want to share. Wait for Steam to send you an e-mail saying your account was accepted (will take a day or longer). Enable Steam Guard on your account as well (apparently it's necessary).
2. On the computer you want to share your games with, log in to your sharing-enabled account. (Read steps 3 and 4 under "Setup Guide (long version)" below for security information about sharing with a remote computer.)
3. In Steam's Settings, under Account opt-in to the Steam beta client and update it. If the update logs you out, log in again.
4. In Settings, click the Family tab on the left. Click [AUTHORIZE THIS COMPUTER...]. Under AUTHORIZED ACCOUNTS, check the boxes next to the accounts that you want to have access to your shared library, then click [OK].
5. Log out. Done!