There is always a risk when submitting an image and there is something similar put in by someone else. Scoring tends to be relative to what is there on the night and a judge might compare the two and downgrade the one which they consider to be the weaker, even though the same judge might have awarded a higher mark on a different night. That's definitely a factor to consider when entering a "Rudolph" or "Tanya" shot, for example.
The other thing to watch is having three images of the same subject as the judge will invariably rank them. It is far better to spread them across competitions and use something else for the other two entries if you are able.
Feedback can sometimes be useful in the quest to improve one's pohotography and on other occasions I wonder where the judge is coming from. Although I have complained elsewhere about the judge who marked a shot down because it was of a genre they did not like, at least they were being honest. Sometimes a judge has picked on a detail as an excuse to mark down an image which they simply do not like. How about lack of detail in correctly exposed glass panels on a small area of the Shard? Just what did the judge imagine would have been there that the photographer had omitted?
Finally, I completely agree with Dave that what helps most in advancing our photography is getting out there and making the shots. There is no substitute for experience.
