Be sure to leave space around the end of one section and the next section’s heading and give plenty of marginal space around illustrations or other points of access. If you’re using columns, leave adequate space between each column of text so that the eye doesn’t “jump” to the other column.
The rule about spacing also works the opposite way: put things that are similar close together. The body text that relates to a heading should be close beneath it. Captions should be directly beneath the illustration or photo they describe.
Above all, strive for consistency in your spacing.
How much space should I use between lines?
The standard you might have been taught for school papers is double-spaced, but different documents require different levels of spacing. In the absence of specific guidelines, shoot for readability. Somewhere between 1.15 and 1.5 is a good place to start.
Some examples of good spacing:
Captions directly below the image.
Images are a good, consistent distance from each other (about 1/2 of an inch here), giving plenty of white space.
Some examples of poor spacing:
Captions placed haphazardly.
Images have no set relationship with any other page element.
Additional Resources
Power of White Space – The Interaction Design Foundation’s guide on the various ways you can use white space effectively in an online document, including discussions of various types of white space, like “macro” and “micro”.
Negative Space in Graphic Design – An article and helpful infographic defining negative space and outlining it’s importance in web design. This site also provides some basic examples in logo design and art.