Laying out a curving path so that it looks good with the topography that it passes over can be a challenge. Here's a method of laying out a path so that you can experiment with the shape and create smooth curves.
Use a garden hose to define a curving edge that is smooth and does not have kinks or straight segments. Since the garden hose is pliable, it makes a good tool for this purpose.
Use two garden hoses to lay out very long, curving paths or border edges so that you can overlap the hoses and ensure a smooth transition from curve to curve.
Secure the hose at a few points with stakes or pins until you have transferred the curve to the ground in a more permanent fashion. This will prevent the hose from springing out of place.
Mark the curve you have defined with field chalk.
Etch or dig along the curve with a garden spade.
Make curves with a small enough radius that you can see the curve as you walk along the path since curves tend to look flatter when viewed this way. Be sure you don't make the curves so tight that they feel artificial as you walk.
Build a curving path by using the curve you have defined as the center line of the path.