If you find yourself using the same database methods etc; over and over then it is a good time to create a MY_Model and place these methods in it.
Then when you create any new model you just extend it from your MY_Model. ( DRY ).
The MY_Model goes into ./application/core/MY_Model.php
What did you Try? What did you Get? What did you Expect?
Joined CodeIgniter Community 2009. ( Skype: insitfx )