In the Format > Paragraph dialog, there are separate settings for Line
Spacing (where you set double-spacing between rows within each paragraph)
and for Space Before or Space After (which affects the space between
paragraphs).
If the Space Before or Space After is set to some number and you don't want
that extra space, set them both to zero. You should do this in the Normal
style (Format > Style > Normal > Modify > Format > Paragraph) for the
document.