惯例 – 据惯例我们每年圣诞节应该去教堂。
I would say: 据惯例，我们每年圣诞节都得去教堂。／都必須上教堂。
（It sounds like 'we' are children, our parents force us to go to church every year.）
（This one is for expressing a custom.）
投资 – just want to say the sentence is perfect!
余生 – 你年龄不小，你必须明智地用你的余生。
"用" is for a certain goal, "用余生" sounds like: it's an old man, who want to make up for someone or something in his remaining years.
"余生" 通常用在這些人身上：an old person; or a person who despairs of something, a person who regrets something, a person who is pursuing something, a person who is immersed in an emotion, until the end of their life.
详细 – 你的报告缺乏详细，再写吧！
like pizzaguy said: 你的报告不够详细
思绪 – 他在认真学习，别打断他的思绪。
绪 is the end of a "thread", or the beginning of a thing or a thought.
剩下 – 我去宴会迟到了。桌子上只剩下了一些不好吃的菜。
Hope these help, instead of confusing you XD