This is mostly a job for the GM and/or world designer. Player characters should not be allowed to create their own sorcery traditions except in the most tolerant of games.
When designing a tradition, always begin with a philosophy.
- Is there any literary or semi-historical precedence?
- How do these guys picture the world?
- What is it possible to achieve under this world-view?
- What is impossible/heretical?
- What is their style? How do they look? How do they sound?
Then try to mesh this with the format of the other traditions, and fill out the following fields:
Examples and References
It is usually much easier for both you and your players to say "Egyptian-Style Cobra Cultists" than to try and describe this archetype starting from scratch.
Limitations
The crutches these guys depend on when casting spells. Usually, this is very much a matter of style. Do you want beard-toting old men in pointy hats mumbling incantations? That can be sufficient limitations in itself, you know.
Common Schticks
What is it possible to achieve under this world-view? What does their tradition allow them to do? Note that having many common Schticks is sort of a limitation, as it limits the versatility of the tradition.
Normally, sorcerers should pick about half their sorcery Schticks from those common to their tradition - until they have them all.
Prohibited Schticks
These are the things the tradition cannot/will not do. In many cases, the use you can put your Schticks to is more limited that what Schticks you have access to - a typical good divine magician cannot summon demons using Summoning, for example, but that is not mentioned here.
Summonables
These are the Spirits that serve the tradition, or that can be coerced into service. It is not impossible to summon other types of entities, but these are the ones included in your lore, whose true names you can find in books. Not all traditions are associated with supernatural creatures at all.