The only garden question that may beat out, "Why did my plant die?" for the most asked award is "What should I do to improve my lousy dirt?"
If you want a quick answer or have a short attention span, my response is to do nothing. If you want more details, I will fill more lines before basically reaching the same conclusion.
I'd start by asking if it is new or old construction. If the house is over five or 10 years, I would again strongly suggest doing nothing. Maybe I would budge a little if you convinced me that you had a heavy clay soil. Most in southern Lancaster County don't.
I'll return to that in a few lines.
Single lot new construction is seldom a problem. Larger subdivisions may be a different story. Often the developer will remove and stockpile the topsoil. When the house is built he will then spread a thin layer of topsoil across the disturbed landscape and sell whatever is left in the pile.
This practice often results in a rather skimpy layer of topsoil and a major disruption of the interaction between the topsoil and subsoil. Compost, tillage and time will gradually heal this problem.
Any soil, especially heavy clay, can benefit from compost. My first choice would be straw laden manure. Beyond that, any organic material will be fine if used properly. I have no problem with peat moss for addressing smaller areas.
Grass clippings often find their way to my garden. The caution here is that their decomposition will use nitrogen from the soil and you may need to address fertility issues on a regular basis. Here, as in any garden situation, a regular soil test is a wise investment. Wood mulches, depending how well cured they are, will have the same but a lesser effect as grass clippings.
For the energetic, make your own compost. Talk to your local extension service or go on line for suggestions. Many gardening magazines and local hardware stores offer gizmos to simplify compost making. A good shovel or fork and a strong back can make a conventional compost pile a fun and worthwhile project.
Well-aged mushroom soil is also a good source of compost. The big red flag here is if it is not well aged it will be red hot with nutrients and will kill plants better than any weed killer I know. Maybe that exaggerates a bit, but beware.
Now let's have a few words about the biggest sin in gardening. Thou shalt not make a special hole for the plant. Anything you add will have a different moisture holding capacity than the surrounding soil.
To keep the drier component moist, the rest is too wet. Repeating, part of the root zone is either too wet or too dry all the time. No plant likes that.
The bottom line is that if you are going to add anything beyond a light coat of mulch it must be mixed into the existing soil very well to be a benefit. Otherwise do nothing.