I have a few preferences, depending on faction I am playing:

As Venice I find this somewhat useful:


____S_X_X_X_S
____H_SSSSS_H
_C__H___AA__H__C
_________________
_______C_G_______

X = crossbows, probably pavise xbow militia
C= Cavalry, I prefer Knights/Heavy cav. Might even be militia cav as Venice has heavy cav as militia.
S = spears (=italian militia)
H = heavy infantry, Venetian heavies or footknights etc.
A = Venetian archers
G = general

The crossbow militia are the first line, but they will quickly retreat to the second line - > flanks when the battle lines close.

The first line spears are there to guard against cav charges, the idea is that they react to any cav threat and buy time for missile fire. The crossbows are not on skirmish usually. The spears take the front quite quickly if the enemy is close.

The heavy infantry is a flank guard, and flanking force when needed. They can also wade into the center if things get too hectic. The second heavies are sometimes replaced by cavalry or crossbows firing to the left/right front side, depending on what I have to use.

The rear cavalty is there to protect the general and to react to surprising threats once the battle lines are closed. Paired with the general it can start charging loose enemy troops - probably missile troops left behind etc.

The Archers are there if I have any. Mostly their function is to have some missile harrasment that works over the battle line. Sometimes there is more, sometimes none.

This works as long as the enemy has no massed artillery, if they do, I use a double line, quite thin one at that. Also, if I am losing the missile fight, I tend to assault swiftly. The main point in the formation is sort of a fist. The footprint can be squeezed tight if or spread out quite flexibly. Also, the archers in the center can fight in melee if needed.