Whatever line spacing you choose, you may want to add extra space between paragraphs. This is especially useful in long documents. A space of around half a line between paragraphs usually works well.
You can specify that paragraph spacing is placed before or after a paragraph. For headings, you should usually specify space above; for the main body of text you should specify space below. When two paragraphs, one with extra space above and one with extra space below, meet, the two spacing values are added together, so you should check your document to see that no gaps larger than you want have been added.