yes good advice about numbers but do avoid the obvious easy to remember ones that could be established by a third party - ie telephone / dob
if you want to create one that is secure then use a couple of seperate items and combine them in a routine that you can remember.
One I used to use was 2F01n5 which is easy to recreate from 3 simple items - my house number, age (a few years ago) and initials. In the end I got used to it and can remember it now!
The routine - x*y-(x*y) the initials translated by the preceding number when inserted, forename caps, surname small.
However we get lax and use really simple ones as Paul had highlighted!