postupiti

1. to act; to proceed
   Postupio si ispravno. — You acted correctly.
   Nisam znala kako da postupim. — I didn't know what to do.
2. (s + instr.) to treat
   Loše su postupili sa njim. — They treated him badly.
3. (po + loc.) to act in accordance with; to follow
   Policija je postupila po zakonu. — The police acted in accordance with the law.
   Postupiću po vašem savetu. — I'll follow your advice.

The imperfective is postupati.