Voochko's second option is the best translation.
Singular:
Budi ono što jesi/Буди оно што јеси (Boo-dee Oh-noh Shtoh Yeh-see)
Plural:
Budite ono što jeste/Будите оно што јесте (Boo-dee-teh Oh-noh Shtoh Yeh-ste)
- with final syllable "ste" pronounced as in "step" or "steady"
It means "be what you are".
You can also say simple
Budi ti / Буди ти
but that's more informal and works only in singular.
Voochko's first option "budite sebe" is wrong because it's translated too literally and reflexive form with sebe/se doesn't work in this case.
Actually if I weren't read the question first, I would think he's trying to say wake up (yourself) although in that case more natural would be short form "se" (instead of "sebe") so
wake up = budite se (imperative, plural)