You can get pregnant again almost immediately after having given birth. The old-wives tales that breastfeeding prevents pregnancy are false (I personally know many women who have breastfed through pregnancy and tandem nursed once baby #2 arrived). If you're not ready to go through the whole process again it is best to practice some form of birth control or contraception.
The New York Times published a handy info-graphic on the effectiveness of different types of birth control. Know your options and talk to your health care provider to see what they think is a good fit for you!