Try offering the bottle when your baby isn't starving. This may seem illogical, but when a baby is frantically hungry, he is going to be in no mood to try something new. He just wants to nurse.

Try having someone else offer the bottle at first. Your baby associates your smell and touch with nursing, and may insist on the real thing if you try to give him a bottle. Encourage the caregiver to cuddle the baby while offering the bottle, but usually it is better to avoid the cradle position.

There is a great article called "Introducing Bottles and Pacifiers to a Breastfed Baby" that will able to answer your question in more detail.