Latching. A good latch is very important for successful nursing. Don't be afraid to take the baby off the breast and start over if he/she is not latched on well. Read this short article for specific tips: http://www.Healthychildren.Org/english/ages-stages/baby/breastfeeding/pages/ensuring-proper-latch-on.Aspx.
Comfort. Get comfortable. Experiment with positions. Bring your breast to your baby. Make sure your baby latches onto the areola along with the nipple. This will prevent sore nipples. Make sure your baby's nose isn't blocked by your breast. Listen for swallowing. If you feel pain, then try it again.
Is it comfortable? Ask yourself this- if you are not comfortable the latch is not correct. However briefly a good latch typically involves mom sitting upright with feet flat on the floor, no clothing in the way and baby at the same level of the breast. Introduce the areola (not nipple!) to the baby. The nipple should be tilted to the level of baby's nose. Baby's mouth should be open wide during sucking.