extjs: Selecting a row in grid once rendered

var grid = new Ext.grid.GridPanel({
    ...
    viewConfig: {
        afterRender: function(){
            this.constructor.prototype.afterRender.call(this);
            this.grid.getSelectionModel().selectFirstRow();
        }
    }
});

See Also: http://www.extjs.com/learn/Tutorial:Creating_new_UI_controls#Method_injection