Practice before you begin. Try your baby carrier with a large, heavy doll or baby-sized sack of potatoes and practice bending (bend your knees), moving through doorways (watch out for his "head"!), quick movements and getting the "baby" in and out. Most of the reported accidents involving babywearing are due to the wearer tripping and falling, so it's important to develop the reflex of holding and protecting your baby when something unexpected happens. Going through the motions in advance can really help with this.
When you start wearing your baby, support her with your arm until you are confident.
Learn to wear your baby carrier properly and get it really comfortable. This is important for your body and for your baby's safety.
Swap positions. Physical therapists recommend changing positions, or changing arms, if you are doing something for a long time. If you are using a single-shouldered baby carrier such as a sling, pouch or hip carrier, this means swapping shoulders regularly (perhaps each time you wear your baby). The sooner you start doing this, the easier it will be. Your baby might appreciate changing positions, especially if you are wearing your baby for long periods. Be guided by your common sense and your baby's cues.
Continue to support your baby whenever you bend over.
Gradually build up your endurance. This happens naturally if your baby is still small. If you are starting out with an older baby, try a few short sessions each day rather than one long one. Gradually increase the duration as your muscles adjust.