How can you write a book easily and stresslessly?

because the ideas just flow threw your head, i was writing a crime story for school and i didn't plan or anything and the ideas just kept flowing into me and i was typing straight away because i knew what to put. sometimes you write it about your life or someone else's life that you know all about so you can write a book about it without having to go to her/his house and asking them loads of questions.