Blueberries are known for being a little more specific about their soil requirements than most other plants, and they generally don't do as well if grown in regular soil with the rest of your fruit garden.
First and foremost: the soil for your blueberries needs to be acidic, around a pH level of 5 or slightly below .
Before you do any planting, you should chemically test the soil since pH isn't something you can easily determine any other way. If your plants are already in place, you can still test the soil and do any amending around your existing plants.
Chemical test kits are generally inexpensive and are definitely worth the few dollars they cost in order to get the lushiest blueberries possible. They are easy to use and just involve taking a small soil sample, adding water, then testing with a colored strip of paper that comes with the kit. Whatever color shows up, it will mean a certain acid level. If your soil is not acid enough for blueberries, you will have to make some adjustments.
The traditional and most natural way to boost the acidity is with added pine needles. Add in some dried needles and take another acidity reading after a rainfall or two. That should help bring the pH back down. If you don't have any handy access to pine needles, you can use any high-acid commercial fertilizer. Check the ingredients for ammonium nitrate or ammonium sulfate for your blueberries. Peat moss can also be added for a boost in acidity as well as improved drainage.
Aside from the acid levels, your bushes will want to have a good supply of magnesium as well.
Besides the soil chemistry, you also want to plant your blueberries in well-drained soil. They do not like having their roots too wet so any location that is heavy with clay is not suitable unless you mix in additional organic matter and sand to improve the draining. Additional peat moss can also add extra drainage to your soil.
Another way to improve your drainage is to plant your blueberries on a slight slope where water will run-off and not pool around your plants. You just need to be diligent in your watering because they will also dry out faster this way.