ことだ
(Koto da)
Used to give suggestions or advice, meaning 'you should'.
Connection rules
- +Verb (Dictionary form) + ことだ
- +Verb (Nai-form) + ことだ
Examples
1.
健康のために、毎日野菜をたくさん食べることだ。

Kenkou no tame ni, mainichi yasai wo takusan taberu koto da.
For your health, you should eat many vegetables every day.
「Doctor's advice」
2.
早く上手になりたければ、練習を休まないことだ。

Hayaku jouzu ni nari takere ba, renshuu wo yasuma nai koto da.
If you want to improve quickly, you should not skip practice.
「Coach's tip」
Practice
If you're having trouble, you should talk to your teacher first.
困っているなら、まずは先生に___。
Romaji also accepted