It is important to identify and understand what your soil is like before you begin your project. Soil maps provide general information about an area. You can conduct simple soil surveys yourself to identify texture (hand manipulation), soil type (jam jar test), pH (litmus paper).
If you are in an urban area, site contamination and pollution may be an issue, and advice should be sought. Consulting old maps in your local library will help you to identify any previous uses for the site.
http://www.landis.org.uk/soilscapes/ is a useful resource for England and Wales.
http://www.fix.com/blog/sifting-through-the-soil/ for simple information on the jam jar test.