Character must roll less than their talent score on a D20 to gain 1 score point. Critical Success gives 2 points.
Learning By Doing - Accelerated (optional)
Character gains one point each game when the skill is used successfully in an important way that had an effect on the game. (Not practicing on a lock in an easy chair) This method works for games that play less often but players want to see characters gain over time.
Skill Training Book
In random finds, characters will find things like "Commerce Skill Training Book".
These will allow the character to solo learn skills without the need of a teacher. (At the GMs discretion) In order to use a Skill Training Book, the character must have a 25 score in any prerequisite skills. Students can not combine them with teachers for a bonus.