I think that the most important to note is that the match engine and how the AI plays has been changed. Previous exploits in the match engine have been fixed and new ones have appeared. The biggest challenge in Football Manager is to create a tactic which works as well in one match engine as it does in another.
One particular style of football which you could have a look at is the famous Dutch "Total Football", which Dortmund and Bayern Munich have taken a leaf from recently and have used some of those principles in their football, this year's Champions League semi-finals being a prime example of how this style can work against two different playing styles.
There are many different philosophies of playing football, but they all have the same principles and beliefs, which is to keep the ball moving and to stay organised in defence, whilst still having enough passing options and enough forward movement. If you can keep these principles, creating a tactic which works in different situations will become a lot easier.
I hope that this has helped