If your code includes any special cases where, for example, no action needs to occur in a function or method, place them as early in the code as possible and order them from most-likely-to-occur to least- likely-to-occur.

For example, in the function ConvertToUpperCase shown below, note that the test for an empty string is coded first. Then error conditions, such as the end index being less than 0 or the end index being less than the start index, are coded after that.

function ConvertToUpperCase( $str, $start, $end )
   {
   if ( $str == "" )
      return "";

   if ( $end < 0  ||  $end < $start )
      return $str;

   if ( $start < 0 )
      $start = 0;

   $len = strlen( $str );
   if ( $end > $len )
      $end = $len;

   return substr($str,0,$start)
          . strtoupper(substr($str,$start,$end+1-$start))
          . substr($str,$end+1);
   }