I waited until I was confident there were no teething issues or any illness brewing. Pick a day when they've eaten a lot. Thus, wait until the day has ended and then decide if tonight is the night.
Normal bedtime routine (for us - a bath, stories, lights out, cuddles then bed).
For the first night of night-weaning I just sat and cuddled whilst they screamed themselves to sleep. Yep, it's horrible, but you're there for them, there's a lot of physical reassurance. They are totally pissed off that their usual comfort has been removed, but they quickly move to looking for cuddles instead of boob. They should go from screaming to whinging to happily cuddling within a week. Offer as much water as they want. Try to quickly move from sitting/lying and cuddling to you standing up and cuddling with the baby upright - cuddles, but it's not comfy for them to fall asleep.
It's pretty knackering for the first couple of weeks as they're still waking quite a lot so I co-slept with both my DSs during this period. DS1 TBH adjusted v quickly (was sleeping through within a week), but DS2 would still wake and cry (depsite my cuddles) for about 3 months.
When they were happily having a quick stand-up cuddle and goiung to down into our cold bed, I moved the whole routine back to their beds. At this stage I would still try to get them down in their own bed if they woke before 11pm, but just broiugfht them into our bed if they woke after midnight.
Don't make going to bed in the dark a sudden thing. We throw the book outside, let DS switch the light off and have a stand-up cuddle. Ds is put down in bed and I leave. I always go to him if he yells. Don't try to to be too quiet - I think it's reassuring for them to hear your voice.