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
regarding 2: this helps you "kill your darlings" more effectively, since it softens the blow of undoing your own work. you're not really killing them - just putting them on ice. and who knows? you might even need them later.