These are high-level, but I think still specific enough to be actionable. These are principles to apply to a design project, and good UX design is reflected in these principles.
Know your users. Have a firm and clear "target" in mind for who you are designing for. Get such insights by conducting user interviews, studying the domain you are designing in, and working with your business stakeholders and subjetc matter experts to identify the audience for what you are designing.
Identify what you are NOT designing. Knowing what you are NOT doing is as important as knowing what you are doing. Define a crisp and short list of what you are going to do and don't get distracted from it. Do two or three things well, instead of eight or nine badly.
Focus. Design with a purpose, and take all distractions out of your view as you work.
Iterate. You aren't going to get it right the first time. Refine, test, iterate.
Simplify. If you think something is too complicated, then the users will probably feel even more so. Strip out everything that is unnecessary and then, after testing it with users, add only things that help and support the experience – not distract from it.
So, to summarize: A good UX deisgn reflects how users think, is simple and focused, and has been refined and tested before implementation.