Have your soil tested. You could go by the general guidelines for your area, but you will be doing yourself a favor in the long run if you get the soil tested. Usually, you send a soil sample for testing to your cooperative extension agency. This analysis of your soil will reveal its PH level and whether it's acid, alkaline or neutral. Some plants like certain PH levels. How do you grow plants that prefer a PH of 6.0 in the same garden with a plant that prefers a PH of 7.5? You have two choices: Choose a plant that will do well in that soil OR prepare soil that will suit the plants you want.
These two videos explain the testing process very well.
Once you have the results, you have scientific feedback on how to prepare your soil for the plants you want to grow.