You can tell what people are like by their mannerisms.
You can get a pretty good feel for a person by the way they carry themselves.
この場合、次のような言い方をすると自然な感じで良いかと思います。
ーYou can tell what people are like by their mannerisms.
「その人の仕草でどのような人かがわかる」
ここでの「仕草」は mannerisms を使って言うと良いでしょう。
ーYou can get a pretty good feel for a person by the way they carry themselves.
「その人の振る舞い方でどんな人柄かが大体わかる」
to get a pretty good feel for a person で「どんな人柄か大体わかる」
to carry oneself で「振る舞う」
ご参考まで!