The practice that can help you past your learned bad habits of trying to edit as you write is what Elbow calls "free writing." (07.6 Passage 2)
主干：The practice...is what...
定语从句that can...修饰主语The practice,从句中的介词短语 past your...habits作宾语you的补语，as you write引导的时间状语从句修饰trying to edite。what引导的表语从句中用了“call+宾语+补语”的结构，what是宾语，free writing是补语。