[RegW]

For accounts that are unimportant to you, it seems logical to learn one complex password that you use across all these sites. However, there is a danger that an account is actually more important than you suspect - perhaps it gives away a clue.

[jcranmer]

That's actually probably the worst thing you can do. Password reuse is a bigger problem in practice than password guessability.

I use password generation schemes. For example, you might decide to use the highest-grossing films of various years. You can then write down the site name and a year in a file and then be able to derive a password, and it gives you dozens of unique passwords that are still resistant to dictionary attacks. It also tends to satisfy sites that require at least one number, one upper-case, and one lower-case letter.