We have never had a prob from day one with DS going into his bed, he's not yet gotten up once when going to bed at night. And when waking during the night (only sometimes) he just sits up in bed & calls out for me...he is 2.5.
We just kept everything as it always was, he's still going to bed so still needs the bath, milk, story etc. We turn the telly off & just chill & then to get him to his room we give him a horse ride on DH back....off he goes.
The one thing I never changed, that often I've heard of people doing (not sure why) but it could have made the difference - and that's the door. We still walk out & shut the door. If need be, I will open it later due to hot weather etc but it was always shut when in a cot, so we shut it now. If he gets up...like in the morning we can hear him. If he was to get up in the middle of the night I would hear & would be able to tell if he was wandering his room in the dark. I think it helps because its dark, the door is shut & he can't see anything so he goes off to sleep. It creates another novelty when they can get in & out of bed & then in & out of the room....just IMO!