The table is ordered by default on it's default field.
You can do this putting an ID column in the grid, and sort on it.
To instance the ID key of the table, just drag-drop the root of the fields tree.
OR
In your view, simply add :
$model->addOrder("a.id");
OR
In the model, change the default ordering key ('pre_order', or something like this, if I remember)
That's all.