Probably the most significant change would be in tactics. Obviously, the tactical notions of the pre-War were...well, not correct, while the War itself was filled with various often very clever (though, of course, largely unsuccessful) attempts to break out of the trenches and "breakthrough". Without World War I, obviously none of that trial by fire would take place, so the notions of the pre-war would remain in place.
That being said, I suspect some of the developments which in actuality took place during and after the war would take place here as well. For instance, motorizing infantry and especially cavalry would still be attractive; without the economic damage and (apparent) demise of militarism caused by the war, perhaps motorization would be rather farther along than it actually was in most countries by the 1920s or 1930s. On the other hand, actual armored vehicles might be less well developed; motor vehicles would, I suspect, not be viewed so much as actual fighting instruments in themselves but instead as transports or (in the cavalry's case) reconnaissance instruments, in neither case coming very close to the fight. Armored cars would still be developed--they were prior to the War, after all--but I'm not sure that tanks would be developed, or at least developed to the same level that they actually were in the 1920s or 1930s by the 1920s or 1930s.
Overall I suspect it would be a rather mixed bag with, as I said, the most notable and important differences being in tactics and strategy, not equipment as such.