If multiple effects modify your hand size, apply them in timestamp order. For example, if you put Null Profusion (an enchantment that says your maximum hand size is two) onto the battlefield and then resolve Praetor's Counsel, you have no maximum hand size. However, if those events happened in the opposite order, your maximum hand size would be two.

Later effects that modify your maximum hand size, but don't set it to a specific number, will have no effect.