Hoi4 is 90 percent planning and 10 percent watching your guys execute. Just look at the numbers along your opponents line and come up with a strategy for attack or defense. There is a tool once you group troops under your field marshals and your generals that paints frontlines. Use that excessively. Don't be afraid to pause to do so. Deliver individual commands as necessary. Trucks and tanks can be split off from your main infantry line to attack specific targets or to literally just cut off your opponents escape by getting around them