KalamaQ has given you a good summary.
Please keep in mind that each organization may have different scorecards. Some may not even have score cards for each quilt, and only the Judge truly knows how s/he comes to the decision. Some shows require the Judges to leave comments with each quilt. Some do not and then they may or may not give a comment, pro or con.
One Judge told me the first elimination she makes is ...
1) is the quilt in the correct class -- correct sizes, correct criteria met
2) is the quilt the same width across the top/bottom and along the sides -- a few quick flips and they have that answer
3) are the corners square? -- very easily seen when doing the flips above
4) is the binding full, tight and straight? -- again, quickly viewed
5) is the general appearance that of quality workmanship? -- are crooked seams, mismatched corners, chopped off points etc. are jumping out from the quilt without really looking for them?
She told me that sometimes it sorts itself pretty quickly with those five ... then after that, there can be a challenge. Or sometimes the challenge is which to bring back from the first ones eliminated, if she does not have enough for ribbon placings.
Even with judging guidelines and scorecards ... a lot is still very much a personal opinion. Anyone entering does need to have broad shoulders as sometimes you will not agree with the Judge! As is the case in many other judged events.