You'd better finish the project by the end of this week.
你最好这个星期前完成这个计划.（不过这个语气强势,如果原句语境是这样的话,就可以替换,相对来说,原句礼貌些..)
Finishing the project by the end of this week is better for you.
原理上可以这样改.但最好的表达还是原句那样.