i'll go first -
1 - you don't have to write your story in order. you can write whatever scenes you want whenever you want, and move them around.
2 - keep a separate "scratch page" document where you can keep the sentences, paragraphs and scenes that you really should delete
omg #1 is something i resist SO MUCH because i feel like i can't keep things in my head unless i go start to finish but i finally broke down with this current WIP and swapped to writing one POV before moving on to the next and thank goodness i did.