Varying your nursing position each time you feed your baby allows different parts of your breasts to be emptied best. The variation also helps take the strain from your back, neck, and arms that can occur if you constantly nurse in the same position. Remember to alternate the breast your baby nurses at first with each feeding. This will help ensure even milk production in both breasts, and make sure that both breasts' milk is drained well several times a day.
While it seems natural that we should be able to bring our children to our breasts and let nature take over, understanding the various positions commonly used in nursing can be a big help for new parents. The initial few seconds of nursing my first baby found me thinking: "this feels like a vacuum cleaner!" The attentive nurse watching helped us reposition, and then, almost miraculously, I felt absolutely fine. At that moment I gained a very great appreciation for the subtleties of various nursing positions!
The most common position in nursing is the "cradle hold." The mother holds (i.e. "cradles") her baby in her right arm while offering the right breast (using the left hand to help). It is crucial to make sure that the baby's tummy in ON your body. If your baby's body in facing the ceiling, or otherwise turned away from you, nursing will likely be painful, and you may not have a good letdown of your milk. Your baby's head, shoulder, and hip should be lined up. While you don't need to check with a ruler, do look to see that no body part is thrown back away from your body. Remember, the better arranged both you and your baby are while you nurse, the more likely you are to nurse easily, comfortably, and well.
Also, use pillows to assist in positioning. One on your lap will raise your baby's bottom up. You may also want one under your baby's head, if your chair's arms are not high enough.
You can try using the cradle hold position while sitting up in bed. I find that a "TV Pillow" (sometimes also called a "Dorm Room" pillow) is a great help for this. These pillows offer good back support, and come with attached arms. At 3 a.m., it can be a true gift not to have to fuss to get pillows positioned at your back, head, and under each arm.
The Cross Cradle
The "cross cradle" hold is a variation on the basic cradle position. While your baby is positioned on your right breast, hold her with your left hand and arm, and, voila, you've mastered another nursing position. This can be helpful if you need to use your dominant hand and arm for something else while you nurse. Being left-handed, I found it easier to use my left hand to help my babies latch-on (LINK A). The cross cradle position allowed me to do that, even when I was nursing on my left breast.
The Football Hold
While relatively few of us compare our babies to an oval of pigskin, the "football" hold is a terrific one to have in your portfolio of nursing positions. Tuck your baby's body under your left breast so that only his head emerging from beneath your underarm. Your left arm and hand do the work to support the baby's body. It is helpful to tuck a pillow under your baby's body, and above the arm of your chair while you sit up.
Side Lying Position
A beautiful position for dozing off while nursing is "side lying." This may be difficult to master in the beginning of your nursing career, but is an absolutely wonderful configuration to allow Mom to nap during, or after, nursing. Lie down with a big pillow behind you to support your back. A body-length or king-size pillow is best, if you have one. Place another, smaller pillow between your knees to keep your back properly aligned. Lie on your side while facing your baby, who should also be lying on his side. A small, firm pillow or a rolled up towel will help keep your baby properly positioned. To nurse, tuck baby (and his back support) up close to you, using your top hand to help your baby latch-on. This position is incredibly helpful for mothers who birthed by C-section and need to protect their incision sites.
"Back-lying" is basically the cradle hold while lying down. If your baby is nursing on your right breast, place a pillow under your right arm, and use your right arm and hand to support your baby's head and neck. This is a wonderful position for babies who frequently splutter or choke a bit during milk let-down. In the back-lying position, the baby, working against gravity, is much more in control of how much and how fast the milk flows (In contrast, when nursing in the "upright" positions, the milk often just falls into a baby's mouth during let-down).
Try to experiment with various positions, possibly inventing your own. Using a sling baby carrier, I was able to easily nurse my little one while walking around. As is so often the case with mothering, using your intuition allows you to find what works well for you and your baby.