Put on the BOM layers you usually wearing in the order you like. When you are done Save it as Outfit. (Right click on avatar, Edit Appearance, Save as..new Outfit.). In same window, Edit Outfit Parts you can move up and down layers to set order. (hover mouse above layer name and an arrow icon apperas to move item up or down in the list.). You can delete all worn clothes and accessories from this saved outfit folder and keep only the BOM layers in it. Anytime you wearing some of these BOM layers SL will know the order by this Saved Outfit. I usually call this outfit "Layers" outfit. If it for clothing layers i would do a saved outfit for each set.