This is not an easy question to answer in view of the longevity of the Ottoman Empire. It lasted over 600 years. With this said, we can point to three important factors, which contributed to the growth of the Ottoman Empire.
First, as with all empires, the Ottomans were a military powerhouse. What made them particularly formidable was that they also possessed great power in their navy. This double power of land and sea served them well.
Second, they controlled many trade routes. For this reason they were able to gain a lot of wealth.
Third, they made peace with the Orthodox church. In other words, they allowed a certain amount of freedom when it came to religion. Had they taken a different approach, great difficulties may have ensued.