In the beginning, it will be hard for both of you. Baby associates bottle with suckling milk, and with your warmth. First attempts to drink from a normal cup will end with spilling on clothes, therefore it's best to start with a training cup (you simply exchange teat for spout), and then continue with a non-spill cup or sports bottle with a straw. These steps will allow the baby to go without stress from bottle to a regular cup, without a lid.
In the beginning, buy a small, handy cup. I recommend buying a cup with a stabile bottom. Your child will probably have a hard time learning to use the non-spill cup - he won't know, how strong he needs to suckle to make the food flow from the spout or straw (you can try taking out the valve from the non-spill cup). Therefore, you must be very patient and supportive.
Learning to drink from a cup is already a stressful moment for the toddler, so spare his nerves from other unpleasant experience during this period. If you're planning childbirth, a longer trip, or moving to another place, postpone drinking training for another time. Don't try to wean him off the bottle radically.
Start by giving him water from a cup during meals, but continue to feed him with milk from the bottle. Slowly substitute upcoming bottle feedings with meals fed with a spoon and drink served from the cup.