hang in there (to persevere; to keep trying; to not give up)
Hang in there! — Держись! Не отступай! Не отчаивайся! Не сдавайся!
Example 1: I know you're four games behind, but you can still win the match. Just hang in there!
Example 2: Hang in there, Leo! Your book will soon be a success.
[stick to one's guns]
[stay the course]
[stand one's ground]