Add shared folder in VirtualBox

In Win7 host, Ubuntu 12.04 guest I tried to add Shared folder, but there are some simple tricks to know.

1. Add shared folder in VirtualBox (Settings -> Shared Folder -> Machine Folders)
2. Make sure that the additions are installed, and that you have added your username as a member of the vboxsf group (sudo usermod -aG vboxsf <your username>).
3. After restart shared folder  /media/sf_shared should be in place

How to install manually guest additions in linux
$ sudo apt-get install build-essential module-assistant linux-headers-$(uname -r) dkms -y
$ wget -c http://download.virtualbox.org/virtualbox/4.0.16/VBoxGuestAdditions_4.0.16.iso
$ sudo mount VBoxGuestAdditions_4.0.16.iso -o loop /mnt