Here is a tutorial / article that outlines the “Horizontal and Vertical” Bezier curve technique. Basically, with a little practice, editing beziers can become a lot easier when you align all your handles horizontally or vertically. While this tutorial talks specifically about illustrator, the concept also works with inkscape beziers.

In inkscape, holding down the alt key is the simplest way to constrain your bezier handles to the horizontal or the vertical.