Tight formations and maneuverability.

The importance of unit formation, before the battle begins, has much to do with the outcome. Total War games place a huge emphasis on unit management. I found myself admiring the beauty and mechanics of the game instead of trying to win. Thankfully Shogun adds some simplicity to the total war franchise by distinguishing between classes of warriors (Ashigaru Samurai, Monk etc) and the types of weapons they yield (Yari, Sword, Archer).

The custom formations Total War provides are not the end all be all to unit formation but should absolutely be utilized by beginners. If you are going to Emulate how I play I can give you a simple rundown of my strategy

1. Always use a clustered formation
2. Archers up front.
3. Calvary far off your enemies flank
4. Sword units ready to charge soon as they are in range of bows.
5. Yari units always near your General.

I play very aggressive with my melee infantry. I do not wait for a prime opportunity, I make one. I want my enemy on their feet as soon as the game starts. I push the attack.

I like tight clustered formations in the beginning because from a management standpoint I can see all my units on the screen, without having to scroll halfway across the map to deal with other units. This adds simplicity when reacting and fanning out before your charge. This of course does not apply to the Cav. Which you will use to flank any exposed unit.