It's not really such an odd idea that handwriting could tell us about a person's character. The brain guides the hand and the act of writing involves eye hand coordination, interpretive abilities and all the other brain functions involved in the art of reading and writing. Handwriting involves both emotional and physical energy. Not unlike body language, handwriting can say a lot about a person and handwriting analysis is sometimes used in settings you might not expect such as workplaces and in legal situations.
The first thing to consider in analyzing handwriting is the darkness, depth and thickness of the writing. Dark thick heavy writing indicates intense emotion and feeling. It may point to the depth of a person's drive and emotions. Light writing may indicate a lack of energy, physical or emotional.
Next consider the slant of the writing. Writing slanted strongly to the right is a sign of an emotional nature. The more strongly the slant to the right the more emotional and open you might expect this person to be. Strongly left slanted writing indicates a person indicates a person who doesn't share emotions easily and tends to keep their feeling to themselves. Writing whose slant is primarily upright shows a person whose mind rules their heart and tends to control their emotions.
Handwriting samples should be done on unlined paper so you can assess the baseline and natural margins of the writing. A baseline slanting upward indicates an optimistic nature while one slanting downward shows a more pessimistic nature. A significantly wavy baseline may indicate emotional turmoil.
The size of writing is also informative. Writing that is very small and neat indicates an attention to details and a conservative introverted nature. Large expressive writing shows an outgoing, outspoken personality who would possibly have trouble dealing with minute detail and tedious tasks. In general large writing indicates a desire to be noticed.
Next consider the letters themselves. Pay attention to the size and length of letters with loops such as (L), (g), (p) and others. Wide loops indicate a person comfortable with people while narrow loops indicate self-control and possible repression of emotions. Straight downward lines show independence and determination. High narrow loops indicated idealism while loops extending deeply into the lower line of a sample show an enjoyment of physical pleasures. If the tops of the letters (m) and (n) are sharp and not rounded it show intelligence and drive. Missing dots over the letter (i) and (j) indicate forgetfulness.
These are just a few of the many traits considered when analyzing a handwriting sample. Handwriting analysis is considered a soft science since there is no way to empirically prove these conclusions, however I found it very accurate when analyzing my own and others handwriting.