The Billings Method has a chapter devoted to it.

Basically you need to really in tune with your bodies signs of fertility and work around that and be quite strict about it. Also be mindful that if your bub goes longer than 4 hours between feeds even once in a 24 hour period then the prolactin levels may not be high enough to hinder ovulation.

I used it quite successfully until Ruby was conceived by then C had weaned though.