Press CTRL+SHIFT+C on PC or COMMAND+SHIFT+C on Mac to bring up the cheats console. Type testingcheats true to enable testing mode.
With testingcheats true enabled, you can enter the following code from the console to set the desired level on a given skill:
stats.set_skill_level [skilltype] [1-10]
As an example, you might enter stats.set_skill_level Major_Fishing 7 to set your skill level on Major Fishing to 7. The list of available skill types is as follows:
While in the cheats console, pressing SHIFT+] can also increase the size of objects. If you enable additional cheats using the testinghcheats true code and then type in cas.fulleditmode, you will enable all CAS abilities. Then you can press and hold SHIFT while clicking on the objects listed below to produce a menu that lets you select the corresponding effect.
Sim - Allows Sim to be modified, except name and inherited traits (Modify in CAS)
Sim - Reset a Sim (Reset Object)
Sim - Add the Sim to the current family (Add to Family)
Sim - All motives are full and mood is Happy (Cheat Motive > Make Happy)
Sim - Motives change dynamically (Cheat Motive > Enable Motive Decay)
Sim - Motives remain static (Cheat MOtive > Disable Motive Decay)
Object - Resets object
Dirty-able Object - Makes object dirty
Dirty Object - Makes object clean
Mailbox - Resets mailbox
Ground - Teleports your Sim to that vicinity