An imperative telling someone to pull themselves together or get a grip; the command form of 'shikkari suru', used to urge calmness and steadiness.
試験まであと二日だ。しっかりしろ！
There are only two days left until the exam. Get a grip!
失敗して落ち込むな。しっかりしろ、次があるよ。
Don't get down over the failure. Pull yourself together — there's a next time.
子どもに向かって『しっかりしろ』と叱る場面もあるが、言い方には気をつけよう。
There are times you might scold a child with 'shikkari shiro', but be careful about how you say it.