What was the war strategy during World War I?
There was really very little strategic thinking in WWI. The only major strategy was the German strategy conceived before the war and called the Schlieffen Plan. This plan called for keeping a small holding force on the border between Germany and France. Then a huge army was to come around the French forces from the north (through Belgium and Holland) and pin them against the smaller holding force. This was supposed to destroy the French quickly.
The Schelieffen Plan did not quite work, largely because the northern army was not made large enough. After that, the two sides settled down to trench warfare. This was not a real strategy. All it was was a war of attrition in which armies made frontal charges in an attempt to achieve breakthroughs. This continued until the US entered the war and changed the balance of power.
I suppose that you might say that the other aspect of strategy was the German attempt to blockade Britain with submarines. By doing this, they hoped to win the war by starving the British into submission. That strategy, like the Schlieffen Plan, did not work.