Sentence

自分の仕事に一心不乱に打ち込みなさい。

自分(じぶん)仕事(しごと)一心不乱(いっしんふらん)()()みなさい。
Give yourself to your work with body and soul.
Sentence

一心不乱に仕事に取り組むのは良いけれど、まわりが全然見えてないね。

一心不乱(いっしんふらん)仕事(しごと)()()むのは()いけれど、まわりが全然(ぜんぜん)()えてないね。
It's good to be able to concentrate single-mindedly on your work, but you're completely ignoring the people around you.