How to get a useful soil sample...

There are many ways to get a soil sample. I recommend sending your soil to a professional lab. You will get more information for your efforts and you'll understand more about the process. I use Umass Amherst for my soil testing (it costs $15 for their routine analysis and it gets busy in the spring so send your soil in early):

You can also have your soil sample sent to these locations as well to be tested:

It's always good practice to get your soil tested before you plan on planting anything in the ground. There’s that saying, “you are what you eat.” Often times in urban environments you will find high levels of lead and other heavy metals. The metals just sit there until you have them removed and amend your soil with compost and top soil. Humans do need metals such as iron and copper in their diets for good health but in small dosages. Large amounts of heavy metals like lead can be toxic to humans and especially children so get your soil tested.

Usually when you get your soil test back it will give you suggestions on how to approach your garden. If the soil tests are high for lead they will probably recommend you don’t plant any vegetable crops and just plant perennials and shrubs in that area. Leafy greens and root vegetables are plants you want to avoid eating when there are toxic levels of heavy metals in your soil.