Read about head-down fetal positions here. Go to the Breech section to read about head-up babies.
The Belly Mapping how-to article may give you clues to your own baby's position.
What is "the most practical way of making sure my baby stays anterior? I've had TWO posterior babies! UGH!”
Mainly, the baby will "stay" anterior if your womb is balanced (symmetrical, not torqued or twisted) and you continue to use good maternal positioning. Positioning without releasing tension in the abdominal soft tissues and pelvic joints isn't likely to succeed in rotating a baby in pregnancy, especially for a woman with a history of posterior babies or breech, because these positions show the uterine ligaments weren't in balance before pregnancy.
There are some myths about laboring with a posterior baby.
Let's start with appreciation for Penny Simkin's brave confrontation of a dogmatic trend that has arisen over the last few years. At first, I was rather surprised to hear a talk by Penny Simkin called, "The OP Fetus; How little we know." Now, the light has gone on. Parents and professionals alike have some misunderstandings about the influence of posterior presentation on labor. For instance, "She didn't have back labor so I didn't think the baby was posterior." Or, "We did everything we could because we tried hands and knees position in labor."
Sometimes a midwife or doctor will say they don't pay much attention to a head down baby's position in late pregnancy because some posterior babies come out fine. Emphasis mine. Spinning Babies is about the 15-30% that need more help than strong labor and the hands and knees position.