The password file I use has 22665 words (it's actually /usr/share/dict/words filtered to 8 bytes or less). I use random 6 word phrases from it, so 86.8 bits of entropy. One word is about like 4.3 digits in terms of randomness, but it's easier to remember. For 12 random letters (56.4 bits) simplest approach is make up a sentence starting with those letters and try to remember it. Here:

>>> import string, random
>>> ''.join(random.choice(string.ascii_lowercase) for i in range(12))
'acobjomepaxr'

So the 12 random letters are acobjomepaxr. A crusty old bastard jumped on my exquisitely pampered, ancient xenophobic rodent. That took a minute to concoct but it helped the words sink in. If you do that, then write down the sentence a few times like before, you will probably remember it. Think of the 100s of lines of stupid Monty Python dialogue that every nerd of a certain age can recite without even having tried to remember it on purpose. Also see: https://xkcd.com/936 .

When I create a new passphrase (6 words using /dev/urandom), I generally write it down on a slip of paper and carry it in my pocket. That is potentially subject to capture but it's pretty safe from network attacks. Then when I need to type it in, I try to remember it but refer to the paper if I have to. After a few times, I don't need the paper any more, so I can drop it into a shredder. I haven't done this recently, but it's not a big deal.