-san is typically generic usage. In my Japanese class, all the students were addressed as their last name + san, as in Smith-san or the like.

-chan and -kun are diminuitive forms. -chan is used towards females and children, while -kun is used for males, usually younger than, close to, or inferior to (in social position) than the speaker.

Usually, any title that denotes respect will be used in place of 'san'. A doctor or teacher will be referred to as 'sensei,' for example, instead of -san, and someone's superior at work will be referred to by their title.

If memory from Japanese class serves.