What element is common to every single layout design, in print, online, anywhere?
Space. It surrounds the other elements, and binds them together. Kind of like the Force. It also lifts and separates, but we’re not using that analogy today.
Using too little space is one of the most basic mistakes of layout. It’s the part of the design that lets us perceive the structure of the information. It’s the pauses between. It’s your ideas taking a breath.
To use space well is to serve the needs of the reader. A wall of text may scare them off, because reading it is hard work. So we break it up into paragraphs, and use headings to organise it so they can find their way around and structure the info as it goes into their head. For that to work, and to look attractive so they want to try reading it, there needs to be enough space around and between the elements on the page.
In particular, headings need space above and below so the eye can clearly differentiate sections of text. What’s the point of putting them in if you don’t give them room to do their job? Yet so many layouts cram all the text together, and it looks awful. The same applies if you use columns of text. Leave a decent gap, so the eye can comfortably differentiate between them.
At the other end of the scale, don’t leave massive swathes of white space unless you’re going for a very stylised layout. Readers may interpret it as wasteful. Even a bit too much of a gap between headings and paragraphs makes them start to lose connection in the mind of the reader. So you need to get a feel for the zone where things work well.
Make it so.