Even with following the rules, and landscaping, there is no certainty that a design will get a reasonable score. I've gotten low scores on builds that I put in a lot of effort, and yet there are unfinished or sparsely built that can get scores of at least 3.5.
BTW, why do some people enter designs that are unfinished, have building sites that are nothing but foundations, and don't even try to follow the guidelines? That makes little sense. Well, I mean, if you are going to enter the contest the least they could do is to level up houses beyond just being a foundation.