Design is often explained in an overly complicated manner, but it can easily be broken down in those three universal principles:
Examples of good websites demonstrate this
That means there are only a few things displayed at once. You will also notice this when having a look at the website examples above. Don’t be afraid of empty space, embrace it and work with it instead. Most junior designers cram too much content in one place. This is rarely easy on the eye.
If there are two buttons, they should be placed symmetrically and horizontally in the middle. If there is something close to the left end of the screen, anything to the right end of the screen should have the same distance. Moreover, spacing between pictures and design elements should be roughly the same. You will quickly get a hold and we will hence refrain from explaining these principles further.
And of course: in design, which is one of the most creative disciplines out there, there is always an exception to the rule. No one has yet found a universally applicable design principle, and opinions are subjective and do change over time. For you it is important to remember: If it looks good, leave it as it is, but be sure that others are of the same opinion. Moreover, use the general principles from above if you are unfamiliar with design. The more experienced you get, the easier it will be to find exceptions to those rules.
Lastly, the more designs you will make, and the more often you compare them to state of the art designs – for instance, derived from the templates linked below – the easier it will be for you to craft beautifully designed decks and websites intuitively.