This first tip is really only of use for multiple lines of text, perhaps the body copy on a poster or single side promotional leaflet.
I earlier touched on the fact that Inkscape is not a fully fledged DTP application, however it does offer a reasonable degree control that means you can achieve many things with text without having to turn to another app. Being able to adjust the line spacing or leading between many different lines of text offers the power to make text fit into a fixed space without changing the font size of the text.
With the Text tool active, you'll see the tool to adjust line spacing as the first of the input fields in the Tool Options bar. You can either use the up and down arrows to make adjustments or input a value directly. Increasing the line spacing can make text seem lighter and less overwhelming to the reader, though often space constraints mean this isn't possible. If space is tight, decreasing the line spacing can ease things, but you should be careful not to decrease it too much as text will start to appear dense and legibility can be affected if you reduce the spacing too much.