What strategies and organization was used in the crusade of Nicopolis?
Like so many endeavors by knights in the Middle Ages, this crusade was not well organized at all. This led to its failure. There was no clear chain of command. Jean de Nevers, 24 years old, was nominally in command. But he was young and inexperienced so Enguerrand de Coucy was supposed to be actually in command. But King Sigismund of Hungary was there as well. So were other knights accustomed to being their own leaders. This meant that no one could really command.
Here, as at Mahdia, the strategy was siege. But once again there were not enough siege engines. So the crusaders simply camped out around Nicopolis and waited. Because they were disorganized, they did not do much to find out about the relief army coming towards them. They also did not create a coordinated plan of attack. Instead, various knights led their men in their own ways because they wanted the greatest glory. This led to a terrible defeat for the crusaders.
The main strategy was siege, then, and the organization was completely lacking.
Again, please consult Barbara Tuchman's A Distant Mirrorfor a detailed account of this crusade.