1.be sure to do something 务必做某事

Be sure to write and tell me all your news.
务必来信把你的所有情况都告诉我。

Be sure to kill your cigarette butt before throwing it away.
将烟蒂扔掉前一定要把它熄灭。

If you know of any others, be sure to mention them in the comments.
如果你还知道任何其他的怪蝠， 请一定写在评论栏里。

2.for sure 无疑

I think he lives there but I couldn't say for sure.
我想他是住在那里的，但是我不敢肯定。

No one knows for sure how serious each of these dangers will be.
谁也不能确实知道，这每一种危险到底有多么严重。

For sure, one’s work schedule has something to do with it –tell me about it!
可以肯定的是，一个人的工作计划表对睡眠一定有影响——告诉我！