When I build my tactics I start with outlining exactly what I want from it. For example, I've lately been playing a lot with a hyper-aggressive, Gegenpressing-style tactic. I used Red Bull Salzburg, Dortmund and to an extent Barcelona '08 as my reference points. I knew that I'd have to have a high line, fast tempo, narrow shape yada-yada-yada.
With my basic tactic created I tend to give it a quarter season to settle in and gain fluidity before I start nit-picking. "I'm conceding too many goals from passes in behind my wingbacks, I should rein them in a little bit." "My centre-mid is neither making incisive passes nor retaining possession; I'll try to get him to play safer. We're impotent in attack now; more risky? That's the one, much better." etc etc.
Ultimately, however, there isn't a "right" which you can get with tactics, as it so often hinges on how your opposition play. Yes your tactic should allow you to impose your game on them but each team will throw up different challenges for you as a manager to deal with, and it is how you deal with these that determines how successful your tactic will be.