I usually start all my designs at a larger scale than what it will be used in the final product. So, I tend to design at a large scale then resize by grouping the layers and then scale it using the scale feature Edit >> Transform Path >> scale. another factor you may have to consider is what way your designs are being structured whther it's with vector images or images which have been Rasterized. If vector, you can re-scale down without any loss in quality. however, if the images (group of layers are rasterized) you may (most probably) get some loss in quality, significantly if your scaling down dramatically.