The most important step is to ensure you can access all the plants in the garden. Either make sure the circle is small enough to reach the center or use a design like a keyhole garden bed to reach the plants. Also, consider light and how tall the plants will grow. You never want large and tall plants to overshadow smaller ones in the circle that may need lots of light. A wooden stake in the center with a string attached can help you make a perfect circle. You can frame your circular garden using paving stones, bricks, wood, or even packed hay.