First, you have to make the commitment to move your child to his own room, or to leave her in your room in a separate bed, whatever you feel comfortable with.
We moved our son to his own room when I got pregnant, around age 2 years 4 months. We would lay with him in his own bed (after making a big deal about his new room, letting him pick out a new stuffed animal to bring to his bed). We would lay with him until he fell asleep and if he woke up during the night, we would go back and lay with him again, we didn't bring him to our bed (and it ended up being a blessing because #2 was a TERRIBLE sleeper and was up nursing every 2 hours until she was 1) and eventually he would sleep longer and longer until one day we woke up and he had slept in his room all night. We praised him each morning and were just really positive about it and now he's 6 and I don't think he remembers that he even ever slept with us, thought we do tell him.