One can't answer this kind of question without knowing what contest you're entering. To win a contest, one must know what criteria the judges use to define a "good" photo. There are many possibilities: technical excellence, realism, emotional impact, uniqueness (finding an unusual perspective of something common, a different lighting technique, or devising an unusual color or tonal look), abstractness, eroticism, narrative/story, mood, humor, etc. Without knowing which criteria the judges value and how they are weighted, any entry you send in is a total crapshoot. There should be some written guidance in the contest rule, and looking at previous winning images is a good idea as well.