I've read that beauty is subjective and I've read that it is objective (I tend to believe a mix of both depending on the context). However I've also read that scientists found that a person generally considered to be attractive or beautiful tends to also have facial features of average size compared to all humans. In similar terms I am trying to approach user interface design. I do NOT at all mean 'a good looking interface will have averaged size controls' as the scientific study I cited was just an example. But what I do mean is, there must be a set of properties or attributes that just make an interface good to look at.
I can look at an interface for a web application and immediately feel disgust or love (contrast for example an early 90s HTML Geocities site against the current Zendesk website, for example). There must be some set of properties or rules that could be defined that make an interface look good. I am trying to learn to design interfaces from scratch as well as take existing ones and make them look great. For example a recent design submitted to me by a team member had everything looking very disjointed and modular, and it looked like crap. I did my best to explain this and eventually they worked on it and made it look great, smooth and... connected? I don't know what terms or 'truths' I am looking for here.
So can anyone tell me, perhaps in a bulleted list with definitions of each term, what visual properties make a user interface pleasing to the eye? It may include color in relation to X (where X is, I have no idea!), or size of controls and elements in relation to available screen space, etc. These are just examples, I do not know what to expect as I do not study design theory, this is where you come in!
EDIT: An example answer in the form of something I can describe would be a plate of food. At a cafeteria if they just plop food down on a plate in random splats it would not be good to look at. At a gourmet restaurant they drizzle things, add parsley, give proper portion sizes and plate sizes to make it look really nice looking. What is the UI design form of parsley and drizzle? I'm serious!