Be sure not to keep or cook more food at home than you need.

一定不要在家里储存或烹饪超出自己需要的食物。

youdao

Be sure to come. Don't let me down.

你一定来，可别拆我的台。

《新英汉大辞典》

You'd better reckon without me, as I am not sure whether I shall be able to be present.

你最好别把我算进去，因为我能否出席还不一定。

《新英汉大辞典》

But remember that you do have recitation on Tuesday, so that could be very helpful with the problem-set, so be sure to go to recitation on Tuesday, and have a great long weekend.

记住，周二有习题课，这对做课后题很有帮助，所以周二一定要来上习题课，周末愉快！

麻省理工公开课 - 化学原理课程节选

Be sure to keep in touch.

一定要保持联系。

I'm sure 课堂 - SpeakingMax英语口语达人

You always want to check your signs at the and because it's so easy to get the sign wrong, and I was hoping that it was right here because I wasn't sure, but it turned out to be right.

我们完成计算时，一定要记得检查符号,因为很容易弄错符号，刚才我就不太确定,是否弄错了符号，检查发现没有问题。

麻省理工公开课 - 热力学与动力学课程节选