WWI is unique in that industrial processes were used to make new weapons. Poison gases that were otherwise byproducts of industry were used on the Western Front as were belt-fed machine guns, tanks, and barbed wire.
For the sake of your question, I will compare WWI with WWII to give you an idea of how weaponry changed. First, there was no such thing as the personal machine gun in WWI--machine guns often had a team of at least three people--someone to aim and fire, someone to keep the barrel cool with a bucket of water, and someone to ensure that the belt of ammunition fed in smoothly. The average WWI infantryman carried a bolt-action Mauser, Enfield, or Springfield rifle, depending on which side he represented. In WWII, men could carry their own automatic weapons--the Soviet Union carried weapons that were similar to the AK-47. WWI flyers also had very primitive planes that did not have aluminum frames--in WWII, aluminum would be a key airplane component. WWII naval craft also used sonar--in WWI, this technology did not exist yet. Of course, atomic weapons and jets did not exist in 1918 either.