Best practices for use of C++ header files

/* Copyright Note and licence information (multiple lines) */
#ifndef FOO_H
#define FOO_H
// Header file contents
#endif

#ifndef FOO_H
#define FOO_H
namespace FooNameSpace{
    // Header file contents
}
#endif

#ifndef FOO_H
#define FOO_H
namespace AnotherNameSpace{
    class AnotherFoo; // forward declaration
}

namespace FooNameSpace{
    // Use AnotherFoo here
}
#endif

// WRONG!
using namespace std;
class MyClass
{
    string stringVar;
};

// RIGHT
class MyClass
{
    std::string stringVar;
};