Interesting things I learned from a friend of mine who works as a legal hacker about passwords:
Making them something you can remember is useful. The XKCD guy's comic on it was sort of on point, but the reality is sites limit you on your ability to use spaces, upper/lower cases, and on top of that the comic itself's password it invented is so commonly used now that it's in password hacking databases everywhere. So, come up with your own sentence that works in most parameters.. Like using !'s for spaces or something for the sentence.
Start with numbers. Most people don't, and starting with numbers can help thwart the stereotypical format for most password hacking codes.
If you have trouble remembering different passwords for different sites and use the same passwords for everything.. Use a stem sentence and change it up for different sites. for example (this is not a password, recommended password, nor what I use): 1eLOVE!amazon .. 1eLOVE!gmail&google ... 1eLOVE!pinterest . etc.. Now, just change some of the vowels into numbers so that you always remember "if it has an a in it, I use a 4 instead.. if it has an i in it, I use a 9" 1eLOVE!4m4zon .. 1eLOVE!gm49l&google .. Or, you can change the name to one you always use. For example, I call google "the oracle" so I could write 1eLOVE!theor4cle .. Stuff like that will create something you can remember (a strong stem sentence) + different components to make the passwords different but easier to remember.
Change your passwords. I'm always SUPER bad about this because I can't remember what sites I use, if I've used them before, changed them before, and the stupid "I'll remember your password for you!!" things never work for me and end up confusing me and cluttering my system. Instead, I just use a wordpad list and change the main ones I remember, write them down, and when I encounter the lesser used ones I change it over to the new password set up and write it down.. so I know if I'm using the old sentence, or the new sentence. Changing it doesn't have to be difficult... instead of "1eLOVE!" I can write "365DAYSilike"
Longer passwords, in general, are far far better than shorter ones. If there's a maximum password set, simply type as much of your 'sentence' as it will allow and make that the password. That way you don't have to remember changing it up into a whole new sentence.
And if you think 12, 12qw, 1q2w, 12qw!@QW, 1q!Q, 1q2w!Q@W aren't in every password hacking database ever you're wrong. Think of numbers that mean something to you but are out of the ordinary for the flow of typing.