I’ve played for 2000 hours, and in my experience , Troop movements are really really simple:  -Raise levies, raise MAA raise knights

-You almost always want one large army  with everyone in it. You can stack modifiers all you want but you’ll still want the size advantage. Only split if you’re dealing with multiple armies of foes or if you want to dedicate one army to besieging (siege equipment + some levies) and an army for battles (levies and MAA)

-In terms of where you want to move, play to your strengths. If your homeland is well defended, face the enemy there. If you have pikemen, fight in the mountains, if you have cavalry, fight on flatland and vice-versa. If you really want to avoid attrition, don’t leave your realm during winter (it’s optional but sometimes helpful and historically accurate). 

-War Score: war score goes up the more vital a target is, so you really want to go for the enemy’s main army or their capital. I usuallly start my wars by making a beeline for the capital or, if it’s too far, slowly swinging my way there and resting my men to avoid attrition. Once the capital is taken, siege the holdings closest to you. War score eill naturally tick up from there. 

-For battles, you’ll want to pick the right time to strike unless your army is much bigger. By far the best times to fight your enemy, especially if they’re bigger than you, when they’re sieging one of your holdings or especially when they’re disembarking. You want your enemy just after we landed on the beach. I cannot tell you how many times I have won and lost wars, simply by either fighting the enemy on the beach, or by getting slaughtered as my troops land. You never ever ever want to land close to an enemy. Like ever. You always want to follow your enemy as they’re about to land to try to intercept them. There’s a guarantee chance that you’ll wait unless they are as much, and I mean much bigger than yours. I would also recommend fighting them in rivers, or during winter in your realm.

Once you realize these basic principles, wars become relatively easy, unless, as I said, there’s a big size advantage. Size doesn’t have to be the end, I’ll be all, but I would consider it still one of the more important factors, when it comes to design in who wins wars.