What I do is make the bezier on a temporary working plane(rectangle or circle) at z=0. (but the z value could be anything). you can actually do beziers on a vertical plane too.
Click starting point, then click ending point, then go back near the start to place the control points and watch for the prompts saying "on face", or edge, midpoint or endpoint if you have other lines on the working plane. Then set your control points sequentially as you please until the bezier ending point.
If you wish to do scaling, Fredoscale seems to work better for non xyz plane orientations, since it will align with the working plane.