every time i try to write one it feels forced and not required to make the song better
you don't need to try to make a key change. if it needs a key change, it should jump out at you, and you will know "this needs a key change!".... one thing you can think about is, where have you heard key changes? go through all the music you own and find the key changes. what are they, and when were they used? you will gradually become accustomed to the ways you like to use key changes. but don't force it