This is an awesome little article by Matt Elliott on CNET. This shortcut is one that I wish I had learned two years ago and had no idea it was possible. I would spend hours writing stuff up in other programs and copying and pasting things to the post pages just so I could avoid this double spacing issue. Read it and use it to your hearts content!!
“I’ve used WordPress intermittently over the years for projects here and there, but it wasn’t until yesterday that I ran into this issue of line spacing for paragraph breaks. I am helping a friend with a state senate campaign site this summer and was updating his events page that listed upcoming house parties and debates.
I wanted to group short lines of text together so that the details of each event were single-spaced, with a double-spaced paragraph break then separating each event. But each time I hit Enter at the end of a line, WordPress double-spaced it, adding an extra line where I didn’t want it.
I tried switching from the standard Paragraph formatting to Address, but that didn’t work. I then tried moving from the Visual editor to the Text editor and adding my own HTML line breaks, but WordPress stubbornly stripped out my tags when I republished the page.
Thankfully, I came across a keyboard shortcut before I pulled out all of my hair. If you hit Shift-Enter, it adds a line break as opposed to a paragraph break, allowing you to create blocks of single-spaced lines.” – Matt Elliott