Handwriting analysis has been used for centuries to help learn more about the writer. What does your handwriting say about you?
First, handwriting analysis works best on adults who have been writing for many years. If you take a class of 7 year olds, it is likely that that class will all write in the same manner, trying to do what they have been taught by their teacher. But as the years go on, each person develops his or her own style of writing, a reflection of their own personality.
When someone is writing right-handed, their writing tends to slant to the right. Also, we are taught to write on the line and to write in a legible manner. So any deviations from these norms are typically indications of a personality trait. If someone always wrote perfectly evenly, very legibly, with the same slant and perfectly on the line, this would indicate that someone has a very precise and perhaps a very conformist attitude.
On the other hand, let's way the handwriting is wildly erratic - sometimes large, sometimes small, sometimes slanting forwards, sometimes slanting backwards. This would not be the sign of someone with great focus! It would show that the person's mind tends to jump around from thought to thought quite easily.
Many times, comparing letters or writings from different periods in someone's life can show changes in emotions. Let's say your sister writes you each month and that the letters are always smooth and flowing, with looping arches and easily read letters. But then say you get a note that has letters that are sharp and angular, done very darkly because the pen was pressed down hard on the page. Even if your sister did not admit to a problem, you could tell that something had changed.
You can even sense deception based on the writing. Let's say your internet lover has finally decided to write you a real letter. His letter is consistent and evenly spaced, down to where he tells you his age. Then there are suddenly strange, larger gaps before the age is written down. This would be a sign of hesitation, that something interrupted his flow of writing.
It's well worth it to get a book on handwriting analysis, and learn more about this fascinating topic!