‘Turn the TV off now, go and put your pyjamas on.’ Give a reason: ‘It’s time for bed.’ Give time for your child to comply, wait five seconds, stay quiet. Stay in the room. If your child does not comply, if you can do so, give them a choice,
Keep it friendly: ‘I can turn it off or you can, which would you prefer.’ Praise your child when they do comply. Don't be tempted to dilute that praise by saying 'Why can't you always do that' or words to that effect. If you do, you will be turning praise into criticism.