standards.txt

Don't expand tabs to spaces.

Tabs should be 8 characters wide.

No trailing whitespace.  A good text editor will have a way to automatically remove trailing whitespace.

Lines should be 80 characters or less.  If you can't make them look decent while that short, the code should probably be split up into more functions.

Functions should have braces like this
{
}

Everything else should have braces like this {
}

An else can be on the same line as the previous closing brace and its opening brace
} else {

Use /* ANSI C comments */ instead of // these dumb comments

Block quotes should look like this:
/* this is a
 * multiline quote */

Put a space after if, while, for, etc.: if (...) {}

Don't put a space after function names: testfunc();

Put spaces around math operators and comparison operators: x = y + z;

Constants and global stuff should be ALL_CAPS.  Give them unique names so there aren't conflicts.

Everything else should be all lowercase.

Don't typedef enums and structs (or anything really).

Pointers and dereferencers touch the pointer name, not the type: int *p;
                                                                 int t = *p;

No magic numbers, if there's something that's not part of some math formula or something so you know it'll never change #define it or use an enum.

Similarly, most strings should be #define'd in strings.h unless it's a log message or something.  Error messages go in error.c along with a unique error code (don't forget to declare them in error.h).

Document what functions do with a comment in header file above the function, document how they do it in the .c file.

Don't duplicate code, if you're typing stuff more than once then put it in a function.

Functions declared in the .c file (ones meant to be private) should be declared at the top of the .c file with their documentation and should be prefixed with a single underscore.

Functions meant solely as macro helper functions (meaning they must be declared in the header file though they should never be called by anything but a macro) should be prefixed with 2 underscores and should be declared directly after the macro that uses them.