How do you plan your armies? Do you just chuck in what you think looks cool? Do you plan on making everything min/ max? Do you have some fluff or theme?

The way I plan my armies is according to the old Tactica I read somewhere about crushing an enemy target fully before moving onto the next target. For example, if I'm taking Black Templars, I have a Chaplain with Jump Pack leading 10 Assault Initiates with the vow Accept the Challenge. I know it's not so much beardy as just a heap of attacks that would potentially overwhelm a small to medium enemy target. Another example is how I play my Tau. I try to have as many troops in Devilfish as possible. I then cruise them down one flank and totally obliterate an enemy position through the sheer number of shots. Again, I don't think it's being beardy, just concentrating fire on a single target.

Although, I must admit, this approach is starting to get stale. I win more often than not and it's getting boring always before the game thinking what I want to do and when during the game. I'm starting to think that maybe I should make my army according to a theme/ fluff.

So, how do you plan your armies?