How to create your own vagrant box out of from existing VM, created by Vagrant?

I created my virtual machine manually using virtualbox.
Then I made a box using
vagrant package --base my_vm_name
Then I got a , which included *.vmdk file and size about 1.2GB, then i pushed it to vagrant cloud

Now I am install some additional software and want to create next version of this box.
I did:
vagrant package
but now i got strange with size 1KB
And it, of course, does not start if you add this file to vagrant.
How to build vagrant box from existing environment, add it to vagrant and push into vagrant cloud as new version?