different shows/contests have different guidelines/rules, and judging criteria. check the fine print on the ones you would be interested in submitting to. but basically; workmanship; visual appeal; balance; color;subject matter and finishing techniques are most often common basics.
some shows/contests have size requirements which must to adhered to or technique requirements...like hand quilted or machine appliqued...you need to read the rules for the contest/show you wish to enter then just do your best work.