Follow the order set out in a recipe. Dry ingredients will often be whisked or sifted together first to avoid overmixing once wet ingredients are introduced. This fluffing and aerating will help the batter blend together quickly. For cakes and pastries, mixing the flour in until ‘just incorporated’ makes for light and tender results. (Making bread is the opposite, where you work the flour with kneading to develop chewy gluten strands.) ‘Creaming’ together butter and sugar helps dissolve the sugar and create air pockets - do this for longer than you think for soaring sponges, 3-4 minutes in an electric mixer. It would take a lot to overbeat, but you are looking for pale and airy, not molten. When using whipped egg whites in meringues and mousses, a gentle ‘folding’ action helps keep the precious air bubbles in.