Planting herbs in your vegetable and flower beds works quite well, as long as you plant your herbs in sunny location with well-drained soil. But you can also design a garden bed devoted entirely to herbs.
When to plant your herbs depends on the plant, but you can't go wrong planting herbs the same way you plant vegetable seedlings; that is, plant them out in the garden after all danger of frost is past. The reason this strategy works for most herbs is that a lot of them aren't especially cold-tolerant. This technique also gets them in the ground under encouraging conditions: warm soil, warm air, and a good summer stretching out ahead of them. They should surge right into robust growth.
If you're considering planting your herbs in an already-existing garden, here are two options:
Herbs growing by vegetables: Adding edible herbs to your vegetable garden is a good idea. They like the same growing conditions of fertile soil and full sun, and when you're in the mood for a spontaneous summer meal, everything you need is right at hand. Some favorite choices include basil, dill, parsley, cilantro, fennel, thyme, and chives.
Herbs mingling with flowers: This type of planting works best for herbs with pretty flowers of their own, as well as ones that can contribute attractive foliage. Imagine not just how pretty the flower bed will be but also the intriguing homegrown bouquets you can assemble if you widen your palette to include some herbs. Favorite choices include sage (including the kinds with colorful leaves), dill, mint, basil (especially the purple-leaved kind), artemisia, and borage.
For many gardeners, the best solution for growing herbs is just to put them all in their own garden. Follow the usual rule for flower gardens; namely, place taller herbs to the back or in the middle of a bed, with shorter ones at the front, so you can see, appreciate, and access everything.
You can choose from many types of herb gardens, but generally herb gardens are either formal or informal. You'd be wise to plan a formal garden ahead on paper, making a geometric design. Install the layout first, with edgings and pathways in place; use bricks, rocks, gravel, or even grass. Edging plants such as small boxwood plants, germander, or a sheared low hedge of lavender or dusty miller also work but require more care.
If you prefer informal herb gardens, take note: A casual bed devoted to all herbs can look delightfully cottage-gardeny, or it can look like a jumble. So make a plan on paper for this sort, too — set it up like your vegetable garden or your favorite flower garden — and then see what happens, making alterations as you see fit. Aim for a harmonious mix of foliage colors and types, with the occasional exclamation point of a flowering herb.