Good landscape design is based on the same principles which underlie any other good design. You can learn basic design principles by taking an online design course or two.
It might be easier to lay out a curving path or plant bed border than you think! Let's assume that the path you are making will be bordered by your plant bed. First you need to select a site. Keep in mind whether you want the path level with the ground, raised or following the contour of the land. You should also consider things like drainage, shade, soil type, air flow, and the type of material used for your path.
Once you have selected where you want to put your curving path or plant bed border, determine how you are going to create it. By this, I mean, if the area is currently sodded, you can simply cut the sod out in the shape you desire just by using a spade or shovel. Whatever the condition of the site, you want to remove any rocks, grass or plants growing there. For a more precise layout, the site can marked by wooden stakes or sprayed with paint in the pattern you have chosen.
Now that your site is free of any unwanted materials, it is recommended that the path be packed down. Before you install the material for the path, you may want to put a small leveled layer of sand in. This will help with drainage and settling. With the site packed, you can now lay out your borders. The borders can vary in the type of materials used such as wood, plastic or tile. For instance, you might want to install plastic or rubberized edging. If you do, then make sure you have enough depth for the edging material if you want it level with ground. Or, adjust the height according to what you desire. You may need to use pegs to keep the edging in place.
With the edging in place, we can now fill the path. The path may be filled with brick, tile, rock or gravel. Which ever you choose, use a level to keep your path even and straight. When doing brick, run your width first, keeping it level, then continue row by row. Make sure you measure up and down as well as cross ways to keep your path nice and level. If the brick sits below level simply add sand under the brick to raise it. Do the reversed if it is too high. Sometimes, it helps to have a rubber mallet to help persuade the bricks into place. After you have laid out your path, you need to fill the gaps between the bricks. Sprinkle sand over the seams then gently sweep the path, allowing the sand to settle into the cracks. Add more sand where needed. This is how to lay out a curving path or plant bed border.
If you're interested in learning more about landscape design, consider taking a design class online.