Some ideas as requested
Germany's use of Zeppelins and 'heavy' bombers to attack civilian targets in Britain certainly set a precedent... They also forced the RFC/RNAS/RAF to divert some of their top air defence squadrons from the Western Front to defend London
Use of aircraft for reconnaissance and artillery spotting was certainly significant throughout the war. It can be argued that this was a factor in keeping the armies entrenched, as it was hard to keep the element of surprise in any breakthrough attempts. If the Germans had had effective air recon. assets, would the tanks have been so effective at Cambrai?
Sustained strafing of trenches was another 'first' but it's hard to say how effective it was. Possibly more of a morale-buster than a troop-killer