There are two schools of thought on passwords. Actually three, but one is just stupid.
First, one that 97% of the population will never get due to the woefully inadequate mathematical training in the public school system...
Second, and this alludes to the first in some degree but some systems force it on you, is to pick something that will never show up in any dictionary, is highly unlikely to be guessed and supposedly is reasonably secure is to pick a familiar phrase where you can use some caps and substitute some numbers for words to create something seemingly bizarre. For instance, "
Your
mother
and
I ate
lunch
together
two
times
this
week" may be easy to remember and translates to "
YmaI8lt2ttw". A sufficiently obscure password for most uses.
The last method, which is used the most, is to pick birthdays, names, places, pets, etc. Those passwords seldom take any password cracker more than a millisecond to break.