That's right, flat design has a "no crutches" rule. All drop shadows, bevels, glows, gradients, lighting effects, textures, and embosses should not be used here, as this limitation is the best way to learn and practice creating flat designs.

If you're looking to create a really flat look, you need to make sure that your design is, indeed, flat. However, don't think that flat is a dictatorship; you can always try to create a flat 3D look, which looks really great, and yes, shadows are allowed. Every designer tries to add and improve the style with their own ideas, and great icons come along the way. The use of shadows and lighting shouldn't disrupt the flat look. So, start by designing as flat as possible, focusing on the important things that make flat design look great. The design includes the grid, the white space, the composition, and the typography; when you feel comfortable, try adding these new elements, as they look really good. There's even a style of shadow,...