The simplest one was for the woman to track her menstruation. Lack of menstruation could lead to pregnancy, so either knowing reliably when menstruation would occur or inducing it was one method. Herbal remedies were often readily available around the house as prophylactics against pregnancy. Parsley, Queen Anne's Lace,* and Pennyroyal were considered effective in inhibiting fertility.
Another way to prevent pregnancy was by inserting something into the cervix. Lacking modern IUDs, Avicenna's Canon of Medicine suggests mint "in there" would prevent conception. Aristotle taught that rubbing the womb with cedar oil, lead ointment or incense, mixed with olive oil, would prevent the sperm from coming in contact with the woman. (The lead ointment had other damaging effects.) Also, wooden blocks were not uncommon, and very uncomfortable.
One could try to prevent the sperm from reaching its goal through a barrier, or one could try to kill the sperm. Medieval and Classical spermicides included inserting a cloth after the act that was soaked in vinegar, or honey, or grated acacia leaves soaked in honey (the sap in acacia is spermicidal).
Another way to "avoid pregnancy" is to pretend one is not pregnant. I grew up understanding the meaning of the phrase "she's gone to her sister's" to explain a long absence.
A French novel (only a little later than the Middle Ages) has advice to a teenage girl about sex, and assures the girl that getting pregnant unexpectedly is easily managed, but not by abortion:
...moreover, to remove any worry, there is one more thing to consider, it is that this mishap is not so extraordinary that one should fear it so much. There are so many pregnant girls who never attract notice, thanks to certain corsets and dresses made to order, which they use, and which do not prevent them from having a good time with those who made them pregnant.
...and during that interval, you can simulate illness, trips, pilgrimages. When the time comes, you will identify a midwife who is obliged in conscience to keep the fact hidden. [L'Escole des Filles]
If the calendar was off, if contraception didn't work, then eliminating the fetus was the next step, but we'll look at that grisly topic tomorrow
*The name is for Anne, Queen of Great Britain (1665 - 1714); earlier names would have been "bishop's lace" or "bird's nest" or simply "wild carrot."
