I strongly encourage every quilter to enter shows.
My advice is to make the best quilt you can, one that you love. You can google to find out what judges are looking for in a prize winning quilt - mostly they are construction tips that simply indicate a well made quilt - straight lines should be straight, bindings full, quilting adequate for the quilt and batting used, quilt designs that compliment the top, etc.
Just remember that the judges aren't interested in hurting any feelings. Usually they will give you a positive comment as well as constructive criticism that you can follow or not.
Good luck!
Janet