korisno

1. (with je) useful; it is useful
   Korisno je znati bar osnove srpskog. — It's useful to know at least the basics of Serbian.
   Bilo bi korisno da pročitaš ugovor pre potpisivanja. — It would be useful to read the contract before signing it.
2. usefully; profitably
   Vikend smo korisno proveli sređujući stan. — We spent the weekend usefully, tidying up the flat.

Most often used in the construction korisno je + infinitive or a da-clause.