You can use :tabmove followed by the tab number to move past. For example, :tabmove 3 will make the current tab move past the 3rd. :tabmove 0 moves to the beginning and :tabmove (without a number) moves to the end.
Another way – though not orthodox – is to enable mouse via :set mouse=a and drag-and-drop tabs around. It might look simpler for a start.