Answer: First of all, you should run some basic soil tests on the soil in your yard. This will tell you what condition it is in and give you a better idea of what you need to be adding in terms of amendments such as lime and fertilizer.
In most cases, it is not a good idea to import "top soil" because the quality of the stuff varies widely and in many cases it is not a good match with the existing soil. This in turn causes even more problems. Instead, it is (almost always) better to improve the existing soil by adding copious amounts of organic matter such as compost, rotted leaves, aged stable manure and bedding, or whatever is available, plus possibly a small amount of coarse sand if you are working with a heavy soil. These amendments help improve the soil structure so it can hold air and water, making it a better environment for plant roots.
For a perennial or vegetable garden, ideally the soil would be deeply prepared, possibly even double dug. Otherwise, loosen and improve the soil at least ten inches deep if possible.
The raised bed is useful in improving the soil and improving drainage; however, the height of it will depend in part on the existing soil and how much amending it requires. You will find that loosening and working the soil, and adding ample organic matter raises the soil level noticeably. Regular maintenance of a two or three inch layer of organic mulch will help to continuously rebuild the soil over time as it rots down.
Your county extension should be able to help you with the soil tests and interpreting the results and may be able to suggest the most suitable sources of organic matter based on the soil you already have.
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