Make up your mind.
"make up one' s mind ""下定决心"
eg: I just couldn' t make up my mind over what to wear to my best friend' s wedding.
我为参加我好朋友的婚礼穿什么衣服而拿不定主意.
I have to make up my mind quickly over/ about where to go for National Day.
国庆节去哪儿玩我得快点下顶决心.