During development, biological systems exhibit large-scale flows coupled to patterning processes, allowing for their self-organisation. In this talk I will discuss two examples of such couplings. I will use an active matter hydrodynamic description of surface flows to explore the dynamics of spontaneous three-dimensional rotation of cell doublets, and how the shape of the cell-cell interface of these doublets can be understood from the Curie principle. I will then discuss the relative role of cellular flows and dynamics of cell fate change in the formation of the vein pattern in Drosophila pupal wings. I will propose a minimal biophysical description of the process of vein refinement to a precise width.