In
40k, there are things that you can control, and things you can not.
What it boils down to is: The only thing you can control is your own army list. This is why most of the "tactical" emphasis is placed on list construction. Through math-hammering, it can be determined which units provide the best performance for their points values. While I do not subscribe to the theory that winning armies should be built ONLY from these efficient units - it does provide a reasonable barrometer of unit performances when building a list.
Every other portion of the game is really out of your control - your opponent's list, the terrain setup, the starting die roll for deployment...
From this point on, all the player can rely on is their own experience. No amount prepatory reading of "tactical discussions" will be able to propel an inexperienced general to victory. LUCK might gift them with a favourable matchup and/or great die rolls, but that would be LUCK propelling them to victory and not anything attributable to any prepatory tactical book learning.
Theory certainly won't hurt, as it MAY help them identify certain broad strategies on the battlefield - it MAY EVEN provide the with the requisite counter(s) - HOWEVER, without actual experience all this book knowledge will amount to naught with a few bad bumps of the dice.
In my opinion, Darth had it right:
Step 1: make a list
Step 2: play a game with the list
Step 3: Reflect on your game and see what beat you
Step 4: Add unit(s) to counter what you lost to or change in game strategy.
Repeat at step 1
You will need to go through this 4 step process about 10-15 times against different lists.
The above is the way that you itteratively increase experience and upgrade your list... however, when it comes to GENERALSHIP... (i.e. controlling your army on the battlefield)... none of the necessary traits can be learned through books.
Inteligent generals are good at coming up with a plan and then executing (and/or modifying) it during the battle. (This includes: objective / target prioritization, battlefield timing, delayed actions etc.)
Wise generals are able to learn from both their mistakes AND the mistakes of others - This is called strength of experience.
Perceptive generals are those who are able to discern the plans and attitudes of their opponents.
IMHO, A successful general is one who combines all the above traits.