1.be sure to do something 務(wù)必做某事

Be sure to write and tell me all your news.
務(wù)必來信把你的所有情況都告訴我。

Be sure to kill your cigarette butt before throwing it away.
將煙蒂扔掉前一定要把它熄滅。

If you know of any others, be sure to mention them in the comments.
如果你還知道任何其他的怪蝠， 請一定寫在評論欄里。

2.for sure 無疑

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.
誰也不能確實知道，這每一種危險到底有多么嚴重。

For sure, one’s work schedule has something to do with it –tell me about it!
可以肯定的是，一個人的工作計劃表對睡眠一定有影響——告訴我！