Our three main destinations were: Zagreb, Split, and Dubrovnik. The touristy attractions in Zagreb are well indicated and all worth seeing. A day trip to the Plitvice Lakes from either Zagreb or Split is highly recommended. From Split ferry trips to Brac and Hvar are a must. THe Sandy Beach close to the Hotel Park is one of the more pleasant beaches and very popular. Dubrovnik is probably the most idyllic place to be. More tourist than elsewhere and everone having great fun.
Quick Tips:
Learn some basic words in the local language. Local people always appreciate if you greet them in their own tongue and then speak English. The Croatians in the bigger centres have no problem with understanding or speaking English. Most restaurants have Optional English or multilingual menus. Say "dobar day" (good day) and switch to Enlish.
Best Way To Get Around:
A Zagreb Card may be purchased at any travel agent and gives access to the trams, buses and a finicular. Even if you only use the trams (which are easy to use) it is worth buying one.
For longer distance travel and transfers we used Dubrovnik Travel and found them punctual, decent drivers and efficient. The Jadrolinja Ferry's (Split) are pleasant to use and not expensive. There is an alternative that makes day trips from Split to Hvar easier -- their ticket booth is right next to the Jadrolinja one.