Hi,
the umask value is used to determine the file permission. Please change your umask value in order to reach your desired permissions. You can do this for instance by adding "umask 002" to $HOME/.profile .
Example: The default umask on Debian is 022. This results in file permissions of 666 - 022 = 644, i.e. rw-r--r--. (For directories it's 777-umask)
To set it to rw for group, you change the umask to 002 resulting in rw-rw-r--.