With a close up lens, or the macro setting of your digital camera, you can get a pretty clear digital image of your flies. If you don’t have a good digital camera, try a flat-bed scanner. Once you have the image in your computer, display the fly at full size. That half inch fly in your vise suddenly becomes 10 inches long on your computer screen. You will notice flaws not visible to the naked eye.
To improve your tying even more, post that picture on an internet fly tying forum and ask for advice. The forums are great places to get expert tiers to give you advise. Be sure to ask for constructive criticism, otherwise most of the feedback will be supportive, like “nice tie”. Ask for improvements, people will help.