Being located in a very turbulent area between much larger nations such as 威尼斯, the 奥斯曼, and 匈牙利, the early game is critical. First aim should be to secure the alliance with Hungary, which is quite easy as bonus is given because the Ragusa is threatened by the Ottomans. Another good ally in the early game is 瓦拉几亚. It is advisable to build up a merchant fleet and send them to protect the trade in Constantinople to secure some initial funding.
The primary targets of conquest should be Dalmatia (part of Venice), as it is of Croatian culture, and Catholic, and will save much on the conversion cost. Make Dalmatia a priority. Try to get your hands on Crete as well, as it will make attacking the Ottomans much easier in the later stages. Next expansion candidates are 波斯尼亚, 塞尔维亚, 阿尔巴尼亚 and 那不勒斯.
After the initial expansion, try to get an alliance with 奥地利 or some of the other big nations, and start attacking the Ottomans. Time the attacks so that at least two of your major allies come to your aid, and while the Ottomans are fighting the 马穆鲁克 and their European provinces are unguarded. Crete will come to the great help here, as you will be able to get a claim on higher value provinces in Greece.
An alternate strategy is to form 克罗地亚. Croatia has superior military ideas, although early formation requires a little luck. Do not ally Hungary; instead, utilize the Ottoman guarantee and join the HRE as fast as possible. Ally 奥地利 and 波希米亚, one of whom should be the Emperor. Pounce on 威尼斯 when they're distracted - you only need to take Dalmatia. Once cored, add it and Dubrovnik to the HRE. If 阿尔巴尼亚 still exist, they are also likely to join the HRE, blocking Ottoman growth.
Expand into 波斯尼亚 and 塞尔维亚, prioritising Croatian cores. Ensure Bosnia or Serbia survive with at least one province bordering you and Hungary. Next, take Hungary's Croatian cores when they're diplomatically isolated; if Hungary warn you, declaring war on Bosnia or Serbia prevents Hungary calling in Austria. It may take several low warscore wars to liberate Croatia. Serbia's ideas, Hungarian and Ottoman cores, and differing religion make it a good vassal, although with potentially high liberty desire.
After forming Croatia, you can convert to Orthodox to gain up to +33% manpower. Expand into 教宗国. If you then pass The Statute in Restraint of Appeals before converting, you keep the bonus for the rest of the game. Conversion requires Orthodox rebels, which you can spawn in any Orthodox province using an unfunded missionary and high unrest.
Colonial expansion is possible, though it will be much more expensive to start the colonies as the starting position is quite far from the other colony-oriented nations as 葡萄牙, 西班牙, 法兰西 or 大不列颠. The good choice is to turn your eyes toward Africa, by colonizing Fernando Po and Cape, Which can be a good stepping stone for expansion into gold rich East Africa and India. This strategy will also be useful when battling Ottomans.