How to write a better strlen function?

I am reading "Write Great Code Volume 2" and it shows the following strlen impelementation:

int myStrlen( char *s )
{
    char *start;
    start = s;
    while( *s != 0 )
    {
        ++s;
    }
    return s - start;
}

the book says that this implementation is typical for an inexperienced C programmer. I have been coding in C for the past 11 years and i can't see how to write a function better than this in C(i can think of writing better thing in assembly). How is it possible to write code better than this in C? I looked the standard library implementation of the strlen function in glibc and I couldn't understand most part of it. Where can I find better information on how to write highly optimized code?