Oneself — a pronoun referring to one’s own person (similar to 'oneself').
自分の失敗を他人のせいにしてはいけない。
Don't blame others for your own mistakes.
彼は自分を律するのが得意だ。
He is good at disciplining himself.
まずは自分の健康を大事にしなさい。
First, take care of your own health.
I; me — a first-person pronoun used by the speaker; often used casually and more by men, though usage varies.
自分、明日休むからよろしく頼むわ。
I'll be off tomorrow, so please take care of things (casual).
『自分はそうは思わない』と彼は言った。
He said, 'I don't think so.'
自分の意見をはっきり言った方がいい。
It's better to state your opinion clearly.
You (Kansai dialect) — used as a second-person pronoun meaning 'you' in some Kansai speech; depending on context it can sound rough.
自分、何しとんねん？（関西弁）
You, what are you doing? (Kansai dialect)
関西では『自分』を二人称で使う人もいる。
In Kansai, some people use '自分' as a second-person pronoun.