I always found that really - you don't, they do.

We did it gradually! We started by putting his junior bed in our room so he knew we were not going anywhere ( might not be possible in some rooms even ours was a tight squeeze )
This is what we have done with Harry. His bed is in our room now and he was utterly thrilled about that - but its a small toddler bed so we could just fit it in. It is still yet to work but thankfully he sleeps through so as soon as he falls asleep next to us, DH moves him into his bed and he wakes up there every morning. Eventually he will get the idea *sigh* Until then its a bit of a tight squeeze at bedtime, lol.