It is interesting to note that parachute units were least successful in the assault role (Crete, Holland (twice...1940 then Market-Garden), even Normandy to a good degree. They were most successful in taking and holding ground in advance of ground troops (sort of very mobile infantry). They also had success in smaller special operations like Eben Emael and Bruneval.
When used as reinforcements by air, Sicily and Salerno for example, they were really just an expensive waste of effort.
So, what changes could the various nations that used paratroops have done to make them more effective operationally and tactically?