Sims love to learn-they are just waiting for a little nudge from you. Sims can pick and eventually master a variety of skills, from writing to gardening to learning how to play the guitar.
Learning a skill is a good way to shape a Sim's personality, especially if aligned with a specific trait, such as the Gardening skill and the Green Thumb trait.
Skills are also a great way for Sims who do not want a traditional career to make money and contribute to the household.Some skills can also be treated as part-time jobs, like growing harvestables or working on a novel.
Development
Any Sim can learn any skill-all it takes is a time commitment and a drive to be the best. Some traits help a Sim master a skill sooner or at least more efficiently. The Bookworm trait lets Sims read faster, which helps speed the process of learning from books.
There are ways to speed skill development though, and some skills actually help out with the development of other skills.
Skills such as Fishing and Gardening are intertwined because the fish caught while practicing the Fishing skill can fertilize harvestables that boost your Gardening skill.
Quality fish caught with higher Fishing skill also boost the quality of recipes cooked while practicing the Cooking skill.
Some skills can be first learned by reading a book or taking a class, which gives you a full level boost.
Learn the first few levels of a skill by doing. When the levels are getting harder to attain, attend a class or pick up a book. You will reduce the time required to reach that next level.
Use public equipment whenever possible to save money. The Athletic skill, for example, is improved by using gym equipment. You can buy gym objects, but why not head to the gym and use their stuff for free? While there, you can also meet other Sims and begin socializing.
Sims learn a little faster when they are in a good mood, so do things that give Sims positive moodlets before and while trying to master a skill.
For example, learning the Logic skill by playing chess at the park can give your Sim the Comfy and Beautiful Park moodlets.
Cheap equipment can slow skill development. At first you may only be able to afford a cheap stove, for example. But when you can afford it, trade up. Your Sim will learn a little faster.
Skill Journal
Sims don't start out with any skills. When a skill is first learned, it is added to the Skill panel, and an entry in the Sim's Skill Journal tracks the development of the skill. The journal charts more than current skill level, though.
Skills that produce tangibles, such as Writing or Painting, have each created work logged in the journal. Other journal entries track time spent doing various activities.
The Skill Journal also details Skill Challenges, which are specific titles bestowed on a Sim if they complete a set of requirements.
Sims who complete a Skill Challenge are rewarded with a special benefit. The journal takes the guesswork out of each challenge because the requirements are expressly detailed.