ww2 was fought differently b/c in ww1 they really didn't have any tanks to speak of, and the tanks they did have were practically usless in battle. for example most ww1 tanks had 4 main guns these guns required crews of about 7-10, and if a tank got caught in a trench it was all over. however in ww2 they created better tanks and they could clear trenches.
Also in ww2, planes and bombers were launched from Carriers at sea. In ww1 Biplanes were used mostly as reconisance and weren't used for dogfights until 1917 and carriers weren't around back then Also the Blitzkrieg (lightning war) was used during ww2 by the Germans. That was simply striking with everything you had as fast as possible. Because of the trenches in ww1, Blitzkrieg was impossible because once troops got into no mans land, they would be cut down by machine gun fire and mortars.