Sometimes plans and doctrines just simply work. The Germans had plans to invade and conquer Poland and France, and it succeeded. The Manstein Plan, to invade France through the Ardennes Forest and Belgium, worked magnificently for the Germans. Incorporating experience from Poland, the Germans used Blitzkrieg tactics and incorporated this doctrine into their battle plan. The few hiccups they experienced, like Dunkirk, were able to be isolated and passed by.
Not to be replicated in the USSR.
Conquering Poland in six weeks was another accomplishment that relied on planning and doctrines. The German Army utilized armored vehicles, mechanized infantry, and other mobile tactics to engage and isolate Polish resistance. While the German Army had not been sold wholesale on the concept of Blitzkrieg, Fall Weiss (the German General Staff codename for the invasion of Poland) still incorporated aspects of Blitzkrieg. Mostly though, it involved multiple attacks across three prongs that would encircle and surround the Polish Armies and end at Warsaw.
Speaking from a bit of personal experience, I can say that the most effective leaders I served under had thoroughly mastered doctrine and could form and execute a plan without issue. A Platoon Sergeant that has his Squads trained in all of the battle drills is confident that Soldiers will be able to deal with any issue for at least a few minutes while things are getting figured out. A Company Commander that runs into a slight hiccup during a live-fire training exercise can easily radio one of his Platoon Leaders and tell them to halt at a Phase Line instead of assaulting because a sister company is coming in to do the assault. In order to improvise, both leaders require a thorough grounding in doctrine and planning.