Your herb garden should be functional and attractive. If you visit other people's gardens, it should help you with your own herb garden designs. There are several important things to decide before you plant your first herb.
Research the plants you are thinking of planting. This will help you understand what types of pests you may be attracting to your garden. Each plant's susceptibility to stagnation and decay when it is transplanted should be another concern.
You must determine what you hope to accomplish with your design. Do you want herbs primarily for medicinal reasons, or are you planting them for seasonings in your food? You can grow herbs of both types, but you will need to plan your garden design accordingly.
How much produce do you need to harvest from the garden? Is the beauty of the garden more important than the actual produce it yields? The answers to these questions are determined by your interests, and you should design your garden with these answers in mind rather than simply duplicating another garden design you have seen.
The herb gardens of centuries past were designed for the necessary functions of life. The garden yielded plants for medicines, seasonings, and dyes. These gardens were sometimes community gardens, and had to cater to several families. Those designs might be different than yours, especially if you just want the garden for the blooms and fragrances.
The amount of space you have to dedicate to the garden will have an effect on the design. If you have plenty of space, you may choose to have every conceivable type herb you can find. However, if space is limited, the garden may be limited to a handful of varieties. The wonderful thing about herbs is the limited number of plants you will typically need for any one item.
How will your garden relate to other landscape features in your yard? Can you plant your herbs in partial shade due to existing trees and plants? What existing landscape features, if any, are you willing to change to accommodate your new garden? Will some of the plants you want to use be a stark contrast to plants that are already there? Are some herbs incompatible with your existing plants?
Where you plant may be dictated in part by the herbs you have chosen. Although some herbs can be grown in shady areas, some require full sun. Some herbs bush into plants and pretty much stay where you put them, while others shoot out runners and want to go everywhere. Keep in mind how the garden will change after you've planted it. Decide what changes you are willing to allow.
Don't be afraid to alter the garden after you plant it. After your original plan is implemented, things may transpire later that make that plan obsolete, or at least not in your best interests. You can relocate plants or have them removed if your interests change.
Freely use your imagination when designing your herb garden. There is no right or wrong place to put your herbs, as long as they get enough water, required sunlight, and proper drainage. Your herb garden designs should be your own and not mandated by the wants and needs of someone else.