I always stick to the same formation, and change the tactics and arrows depending on my opponent. The players play in the same positions, and more regularly and improve more.

I put 2 down arrows on CM and go defensive with long ball and all that stuff...or go down the flanks if they are weak there. I had on all my games this season till this morning (but the guy had a better team and 13% possession advantage). So I exploit the weaknesses with all that stuff.