How do the subclass skills gain experience?

During the beta I never found a direct connection between kills and the experience that the different subclass skills were gaining. For instance, if I wanted to focus on leveling up my jumping skills, how do I go about doing that? What about my grenade skills? [b]Please do not respond with a random guess. Include some kind of supporting information or a link to your source. If you don't know, don't answer.[/b]