It's often useful to think of two general types of white space: unused and deliberate. Unused white space is there simply because you've not put anything there. It's just an area of a page where nothing is. On the other hand, deliberate white space is put there by you specifically to create a gap between the things on the page. A general rule of thumb is that unused white space is bad and deliberate white space is good. (This isn't always true but it's a good rule to learn.) Keep an eye on your white space and keep thinking "Should there be a gap there?".