Maybe good to prepare:
- Letter of invitation from you with your name address, dates and that he will stay with you in that period of time;
- Funds to show that his trip is covered (bank statements);
- His return plane ticket to show he's returning home after the trip;
- Any information that he can present to show his current ties with his home in Croatia, home ownership, etc.
They may not be necessary - but good to have prepared.