Any rangend unit has to aquire these things in order to be effective.

1) Hight advantage (self explenatory)
2) A good direction (Use archers from rear, and from sides on which thay don't carry shield. Ultimatly, if you realy have to use them from the front, try to place them as far as you can to the left of you battle line, so they have a chance to hit the side of enemy that doesn't have any shields).

My usual setup is to have a battle line od infantry and then to wheel around the enemy flanks with archers protected from enemy by my heavy calivary (only if enemy has less of it.). Shower the enemy with arrows and their morale shoud drob considerably even without fire arrows. Also idiotic AI hleps when he places himself stationary ad doesn't want to atack so he's just asking to get encicled by archers and sent to death by arrows.

This is done a lot easier with HA. Shure, don't let them get into fights with normal archers but then again if you place your battle line on the other end of the map, enemy will likely leave the archers alone to deal with your HA, which exposes them to HA charge (which isn't much powerfull, but it's strong enough to disperse archers (is they are not havy Superman Dvor archers, who can rank as medium infantry and have a devastating arrow attack, as strong as srossbow and has aq fire rate of a bow)) and rout, and then proceed to destroy other enemy problematic targets (Light Calivary (the have small defence, so the fall like flies when exsposed to heavy HA fire), spearmen (dangerous to your all calivary army, but weak from the rear, and ideal for destruction by HA. Peper them with arrows untill they start to get scared and then harge into the rear)), and in teh end everything else untill you run out of arrows. In the end battle ends with a devastating charge of all your troops after which enemy will break and start fleeing and it is up to your HA to catch them and put them to death (even a general will have problems escaping superlight HA).

Just my 2c. But tis is on Medium dificulty. On higher the enemy gets bonuses.

And one of my tests. I used an army of 6 Dvor archers [dismounted] + General (only ther to chase routers. Will not participate battle), and I pittet against them all kinds of infantry in the same quantity. The result was allways the same. If the Dvor get a hight advantage, put a line of dvor on a hill and have two flanking Dvor units away from it. The fire from those flanking units (they fire in the exposed sides) and the autofire from the battle line will withle down the enemy to 70% or even 60% untill they approach teh line. And I didn't retreat. After they come into combat Dvor is still a god inf unit and will inflict still considerable losses on the enemy, while flanking units fire in the backs of the enemy with flaming and normal arrows (3 normal: 1flaming is a good ratio). The battle usualy ends with Dvor taking not more than 30-40max% of casulties, while enemy is simply beaten to the pulp.