I would suggest taking a look at Web IDE, the provided master detail template would generate a function to do this for you. Depending on the chosen template it would look like
selectFirstItem: function() { var oList = this.getView().byId("list"); var aItems = oList.getItems(); if (aItems.length) { oList.setSelectedItem(aItems[0], true); this._selectedItemIdx = 0; } },which is called by the list updateFinished event.
Regards,
Jamie
SAP - Technology RIG