Have Javelin tossers hold fire until the enemy is within spitting distance. This is more effective then letting them fire at will at whatever distance they feel like. It's also quite a morale hit if a lot of their troops die quickly, which is what will happen if you do things this way. Ordering your infantry to hold fire also has the side effect of making your infantry hold their shield in a more protective position (try it and you'll see what I mean)

Some people consider Bowmen complete shite in VC. One thing they are definitely good for in my opinion is preventing a long row of rock tossers from going to town on your shield wall completely unimpeded because rocks throw farther then javelins. Having some bowmen firing on their "tossers" will generally force the AI to charge into your Shieldwall.

That reminds me.... Have your infantry form a shield wall! Order them to bunch up or spread apart depending on the situation. Instead of ordering a charge, have your shield wall advance 10 paces at a time to ensure your have a nice uniform wall of death. When you notice a large proportion of the enemy running away, then order your charge.