If on very flat terrain, advance slowly with X-bows while sergeants flank quickly to draw fire. Also, moving you spearmen just within easy range of enemy archers and holding a shield wall will draw fire away from your X-bowmen where they can break themselves on your spearmen shields. Keep them just in range and pepper them with bolts.
At the same time, you can safely advance in a fast charge with sergeants/spearmen - their durable shields will protect against arrows and spears will apply major pointy hurt onto your foes while maintaining safe distance. This itself will significantly reduce enemy numbers. Rhodok X-bowmen are the most powerful ranged NPC units in the game, and it is always convenient to begin a ballte by darkening the skies with crossbow bolts. A single Rhodok infantryman is probably the worst unit to fight with - use thme en masse however, and cavalry beware.
