Start with a preset that suits your players or your preferred style. Personally, I build on the players I have rather than impose my own style.
The, you have to give it time to become cohesive - 'a few games in' won't cut it, you are playing a long game here and it will take some time to tweak.
At start of save, arrange around 8 or 9 friendlies. Set your overall tactic, and watch the games in full (many recommend 2d view for this) Look at where you concede from and where you create chances. Where you control the space and where you don't and add/remove TIs and PIs as you see fit. Key is make small changes and watch the result.
Be patient is the key. Not only patience with the tactic, but also your understanding of the game. It sounds as if this is your first tactic from scratch, so it will take a while to get your head around the nuances.