We're going through this right now. DD has been trying to drop one of her day sleeps for a few weeks but silly Mummy has only recently figured it out. The first thing I noticed was that her afternoon sleep started getting shorter and she started playing for longer in her cot when we put her down before having a sleep. Then the morning sleep was pushed back half an hour too. Meanwhile I just kept to the same old routine and because she didn't fight it, I didn't realise. Then she suddenly stopped sleeping in the arvies and would just play in her cot for 45mins - 1 hour and then crack it to be gotten up. And the main trigger - she was totally fine despite the lack of sleep.