One important bit is how you control your army. In RTW gameplay is quite fast both in terms of speed and combat resolution. It can be slowed down to allow more control by home moding the terrain modifiers. Most major (and minor) mods do that.

Another potential way is to give high defence values on average but that takes too long for home modding to balance the game.

Another way is to play in the highest unit sizes - that slows combat resolution and gives you more time in the heat of the battle for maneuvers.

Generally its best to control your army by groups. One for melee infantry, one for missiles, one for cavalry and one for the general. Unfortunately in RTW groups are fixed in space, so every time you pick them they arrange themselves in the way they were when you grouped them which may be actually not good if they have taken casualties or some are missing due to have routed etc.

For major strategic moves of army components, using the groups is best as they moving together ensure that units don;t get isolated numerically and so they don't suffer morale penalties, and also in this way you don't really have to see all units on screen to know what they are doing - you know they are in the group and move with it. You can micromanage them as action happens from the screen - say for oredring a charge etc. Again slowing down the speeds helps with that to have a better experience due to the pace as you can command most or all of your units during the height of the action.