Passphrases you can actually remember
Random words from the EFF's 7,776-word list, picked on your device. Six words are about as strong as a random 12-character password, and far easier to type.
When to use a passphrase
Use one where you have to type it yourself: your computer login, your password manager's master password, a Wi-Fi network, or an account on a TV. For everything else, a password manager filling in a random password is simpler.
The strength comes from the words being picked at random, not from you choosing them. A phrase you make up, like a song lyric, is much weaker because attackers try common phrases first.
Word list: EFF Large Wordlist by the Electronic Frontier Foundation, used under CC BY 3.0 US.