There are several detailed how-to posts about this. If you are an advanced user, you can use resize2fs to grow your image up to 2GB. You can also make a partition on your SD card and copy your image file into the partition.

A slightly less advanced option is to make a directory on your SD card for your apt cache and then mount it in your chroot. You have to do this each time you reboot or close the chroot, however...

If you are not that advanced, and you've done what I suggest in the Easy Debian Turbo thread's first post (use localepurge etc to get back a lot of room), then you'll have to start removing applications.

EDIT: The partition post is slightly outdated. Use gtar instead of /home/user/img-install/tar, and I would recommend running "sudo debian" to mount the image rather than "mount -o loop ..." like suggested in the linked post, since that way you can use the turbo loop.