I recently played against two opponents who weren't very strong at the time, and I noticed something. A Knight significantly reduces the difference in development. Here, I built something, and they built something. On the King map: I used soldiers to break through first, then I took and built. They just clicked through. That's the essence of the difference.
Regarding tactics:
Build Griffins. Just take a Warrior and take castles by using a large number of these Griffins. That's the whole tactic.