usavršavati

1. to perfect; to improve
   Svaki dan usavršava svoj engleski. — He works on perfecting his English every day.
   Firma iz godine u godinu usavršava svoje proizvode. — The company improves its products year after year.
2. (usavršavati se) to improve one's skills; to undergo further training
   Lekari se stalno usavršavaju na kursevima u inostranstvu. — Doctors keep training on courses abroad.
   Želim da se usavršavam u programiranju. — I want to keep getting better at programming.

The perfective counterpart is usavršiti.