When I define an issues view, the items sort by ID (ascending). I would like to arrange the items according to Priority (per default without having to click the Priority column). Is it possible to add some lines in the view definition to get the list arranged in this way? 

By default, Issues are sorted by ID (ascending). You can then change the sort on-the-fly by clicking on the column header for the field you wish to sort by. It is not possible, at this time, to script a different default sort in the Issues view.