Change the default number of rows to display on one “page”

For DataTables version 1.10.5 and newer, as documented on the blog post announcing the integration of HTML5 data-* attributes, the number of rows to show per page can be specified via the source (HTML) table through the data-page-length attribute:

<table data-page-length="25">
     ...
</table>

For DataTables version 1.10 and newer, as documented at Reference > Options > pageLength, the number of rows to show per page can be specified via the pageLength attribute:

$('#example').dataTable( {
    "pageLength": 50
});

For DataTables older than version 1.10, as documented at DataTables > Usage > Options > iDisplayLength, the number of rows to show per page can be specified via the iDisplayLength attribute:

$('#example').dataTable( {
    "iDisplayLength": 50
});

My two cents: use the data-* approach. It allows you to construct one dataTable call (that you can use throughout your app) while providing the option to configure how each individual table behaves:

<!-- table with embedded custom configurations -->
<table class="apply_dataTable" data-page-length="25">
     ...
</table>

<!-- table with different embedded custom configurations -->
<table class="apply_dataTable" data-page-length="50" data-order="[[2, "desc"]]">
     ...
</table>

<!-- one JavaScript call enhances both tables above -->
<script>
    $('table.apply_dataTable').dataTable(); //one invocation of datatables treats each table they way it wants to be
</script>