Routine is the key. It all goes out of the window over holidays of if the little one has been ill.
You can't overestimate the importance of routine and keeping calm. It is so easy to get cross and p-ed off with them!
A crying child won't die, but the stress on you will be worse! Be kind to each other, sit down with a cuppa and your favourite box set of comedy. Don't get stressed. You love your child and want what's best. Remind yourself that you are good parents and its just a phase!
Yes, you are probably tired and want to get on with grown up stuff/crash on the sofa with a cuppa but... Well, kids, eh? They press those buttons every time!
Start the routine early. Maybe even a couple of hours. If your child is time aware, or you have a night time clock then show them where the clock hands and and talk them through it - this is bathtime, then we have a story/smuggle... Whatever the routine is.
Try not to have drinks in the run up if that will cause numerous loo trips! Avoid stimulation - a tickle fight before bedtime is not to be advised.
Think about what you want and how you can get there. A child won't conk out in ten minutes on night one. Even if they stay in their room all night, that can be a win!
A child wants your attention. If they are ill, scared, etc, then that's a genuine thing - otherwise you need to beel calm and 'business like'. Don't get into long, involved chats or interactions - this is what they want! If a child keeps getting up 'back to bed please' and withdraw. A child crying - check there is no 'need' (dirty nappy, thirsty etc) - don't turn on the light. Be firm with them, tell them what you need them to do.
Older children will need some sort of 'point' system' - whatever works. So if they have 60 mins computer time, start a mental taxi meter running, so count out when they kick off - calling out to get attenion is 30 seconds, 1 or 2 mins off computer time. Jumping out of bed to stomp about is 5 mins, etc. Tell them so that they know - write it down. They will kick off at first but do quickly learn. They can also 'earn' minutes back - this is the beauty - if they make the bed in the morning, that's 1 minute earned! They are only small amounts, but it works - same can work with pocket money - a penny at at time, or half a penny. Again - can be earned back for 'positive behaviour'.