回答

・I'll be serious (about it) from tomorrow.
・I'll do my best from tomorrow.
・I'll try hard from tomorrow.

【I'll be serious (about it) from tomorrow. 】
明天開始要認真了。＝明天開始認真對待。

serious about something = 對..認真

例）I'll be serious about my diet from tomorrow! So, for now, it's ok.
　　明天開始我要好好減肥，所以現在吃點東西沒關係。　

【I'll do my best from tomorrow. 】
明天開始我會盡全力。

do one's best/ try one's best = 盡最大努力＝認真做　

例）I'll do my best for my diet from tomorrow. Right now, I don't care yet.
　　明天開始我會認真減肥，現在我還不擔心。

【I'll try hard from tomorrow. 】
明天開始我會努力。

try hard =努力。

例）I'll try my diet hard from tomorrow means all-I-can-eat for now.
　　明天開始我會認真減肥，所以現在是吃到飽的時候。

吃到飽＝all you can eat
這裡我開了一個小玩笑，故意把 "I" 改了一下，表明因為我明天會開始認真減肥，所以現在可以隨便吃。不好意思，讓大家見笑了。

有幫助｜0