poboljšati

1. (+ acc.) to improve
   Moram da poboljšam svoj srpski. — I need to improve my Serbian.
   Nova uprava je poboljšala uslove rada. — The new management improved working conditions.
2. (poboljšati se) to improve; to get better
   Vreme se konačno poboljšalo. — The weather has finally improved.
   Njegovo zdravlje se poboljšalo posle operacije. — His health improved after the operation.

The imperfective is poboljšavati; the intransitive meaning needs se.