One of the hardest things when evaluating your own work is letting go any personal attachments you have with the image. In particular, you have to try to forget the feelings you had the moment you pressed the shutter, the excitement, tension or fear surrounding the shot. To see whether a shot “works” and a photograph, you have to put that all aside and try to evaluate the image as would someone who wasn’t there when you pulled the trigger.
This is the reason why many photography teachers and writers advise you to put aside critical editing decisions till some time after you took the photo. Feelings will have faded and what is left is hopefully a more considered look at what is actually there in the image rather than what you can remember having felt at the time. If the subject matter is personal, then you may have to try to put aside as much of that as you can.
It sometimes helps to go back to the basics, composition, exposure, and focus. Concentrate on whether these elements help or hinder the image. It’s not a matter of “good vs bad”, rather a matter of whether they are appropriate for the subject. As Ansel Adams is often quoted, “There is nothing worse than a sharp image of a fuzzy concept.” Most importantly, does the image say something and if it does, to whom is it speaking? It doesn’t matter how hard it was to get the shot if the shot itself is not interesting.
It is useful to find out what other people think, not as a replacement for your own judgement but as a complement. People respond differently, they necessarily come to a photo with their own background and experiences so what they see may not be what you see. But there are also common points of contact, universal resonances that should be apparent in the best photos. But it is important to not take any criticism too personally, take what constructive suggestions you can and file away the rest as a learning experience.