@ Al

I think, there's no way, that everytime works. It depends on so many factors... but I'll give you my experience:

I play only new version, because many times I'm not at home, if I have a game.
I usually start with 4-5-1V, defensive, counter. (Other formation only, if I face a formation I know, it doesn't work. F.E. My team can't win vs 4-4-2 classic with 4-5-1V, so there I change).
At minute 20, I go to homescreen and back to game, check the current stats. If the opponent has much more shots on target, I'll turn off counter. I also read the AM-Hints.
1. scenario: Things don't go well, I make some changes, but this depents on: my players rating, opponents player rating. Maybe I make a sub, maybe I set some arrows, maybe I change position.
2. scenario: If things go well, but I conceed a goal, I'll stay the next 10-20'. After that, I'll go out and check stats again.
- If the stats are with me, I'll stay again next 10-20'.
- If not, see scenario 1
3. scenario: Things go well, I take the lead, so I have both eyes on the opponents formation. If he change something, I'll try to guess, what he's doing, to set new tactic or change some position.

F.E. CL-quater finals:
I took the lead at 13'. At 22' his team scored, but he didn't change his formation, so I went on. Last highlight before I wanted to switch out, I conceeded 1:2 (38'), so I checked stats and saw, it didn't work. At halftime, I changed formation, made one sub. Finally I won 4:2.