YOU SAID:

please let me be good at one thing

INTO JAPANESE

私は1つの事をよくするようにしてください

BACK INTO ENGLISH

I try to do one thing well

INTO JAPANESE

1つのことをうまくやってみる

BACK INTO ENGLISH

I will do one thing well

INTO JAPANESE

私は1つのことをうまくやる

BACK INTO ENGLISH

I will do one thing well