S.C.
My daughter was a co-sleeper since birth. I refused to do cio and knew when she got old enough to understand, I would start putting my foot down on her sleeping in her own bed. This is what I did.
After books, we snuggled for 2 songs (came bedtime CD every night). After that I would sit on floor at foot of bed till she fell asleep. After about a week I changed sitting on floor for about 20 min. After about another week I stopped sitting on the floor. I would answer a few questions she would yell out for a few min. I would tuck her back in twice if she got out. After that I told her I am not talking anymore and if she got out of bed I would close her door (very big thing for her to have her door open). It worked. She would still try and talk to me in the beginning, but when I wouldn't answer, she gave up.
I started this when she was 3. She's a few days away from 5 now and we still do books and snuggles for 2 songs.