Make sure that your travel documents are in order before making a trip to Croatia. The citizens of most countries like the U.S., Canada, The E.U., Australia, and New Zealand need only a passport with at least three months validity beyond the intended stay. Check with your local Croatian embassy to find out if you need a visa or not. Usually for stays up to 90 days, no visa is required.
If you are a citizen of a country that needs a visa or if you intend to stay for more than 90 days then go to your nearest Croatian embassy and apply for a visa. Application must be done personally for the visa and certain requirements are needed before a visa is issued to you.
Aside from the visa application form you need to have with you a travel document and a passport size color photo. You need to show documents that prove the purpose of your visit to Croatia, your accommodations and covered expenses, your intent to return to your homeland and your means of travel.
Once you have accomplished all of these, the visa is placed in your travel document and is issued with a validation date. If however you are denied a visa, the officer in charge of your visa application may not disclose to you the reasons.
Upon arrival at Croatia, you must register with the police however long you intend to stay. Hotels, hostels and other commercial accommodations automatically register their guests but if you are staying with friends or in private accommodations then you have to register yourself to avoid fines or deportation.