Positioning is very important when wearing your baby or child. If you get a baby carrier, please take the time to practice how to wear it correctly so it is safe for baby/child and also comfortable for you the wearer.
Some carriers do take a bit more practise to get right, like mastering a woven wrap technique but once you have mastered it, it is another great tool to use when baby is upset.
Slingbabies has a great page about positioning so have a read.
Please also read this useful link from Babywearing International about baby wearing safety.