In general:
For minor changes to a function, copy the existing formatting.
When changing the style, commit that separately from other changes.
For new code and major changes to a function, switch to the official json-c style.

Official json-c style:

Aim for readability, not strict conformance to fixed style rules.
Formatting is tab based; previous attempts at proper alignment with
spaces for continuation lines have been abandoned in favor of the
convenience of using clang-format.
Refer to the .clang-format file for details, and run the tool before commit:

    clang-format -i somefile.c foo.h

For sections of code that would be significantly negatively impacted, surround
them with magic comments to disable formatting:

    /* clang-format off */
    ...code...
    /* clang-format on */


Naming:
Words within function and variable names are separated with underscores.  Avoid camel case.
Prefer longer, more descriptive names, but not excessively so.  No single letter variable names.

Other:
Variables should be defined for the smallest scope needed.
Functions should be defined static when possible.
When possible, avoid exposing internals in the public API.