Dear Varghese,
It's obvious that no free space left in data segment, as I recommended before, you have to add space by using "ALTER DATABASE .. "
Regarding how to prevent default segment from being full, in addition to what Jeff has recommended, you can think of the "auto extend" feature which allows you to automatically expand the database size when free space decreases to a certain level.
For more info. about how to set your database for auto-extend, check that link:
Regards,
Peter