I've been reading up on a number of tactical articles and books ranging from Napoleonic era manuals and treatises to modern day tank battles and maneuver warfare. It's been a lot of fun and I've discovered that, regardless of era or technology, they boil down to a few, specific principles. First, use the bulk of your army against a smaller chunk of the enemy. You can do this through maneuvering (movement and better positioning to keep the rest of the enemy out of reach) or through stalling or trapping one side, or even by using firepower, speed bumps and sacrifice units to keep the part of the enemy army that you wish to destroy first cut off from the rest of the enemy. I present to you several thousand pages of reading, condensed in this easy to read format. Enjoy!
Picking your Battles
How to outnumber the enemy even if there are just as many of them as there are of you. This idea is based off of one of Napoleon's strategies and involves using a sacrifice unit to hold off the rest of the enemy force, at least briefly, while the bulk of your forces smash a small section of the enemy, leaving your units in better position to defeat the rest.
1 unit slows down 2 enemies while 2 units smash 1 enemy unit, then pile into the next one.
Do the math: Each side has 3 identical units. Each unit can take 2 damage points, and will cause 1 during every combat phase.
From Right to Left A, B and C are your units, and the enemy units across from them are 1, 2 and 3, respectively.
Unit A charges enemy unit 2, causing 1 point of damage and receiving 1. Units B and C both charge into enemy unit 3, taking a point of damage and wiping it out.
During the enemy phase, enemy unit 1 charges in against unit A, causing another point of damage and killing it, but not before it does a point of damage to enemy unit 2, killing it in turn.
During your next phase, the remainder of units B and C pile into enemy unit 1 and cause 2 points of damage, while taking one in return.
Final result: you have a full unit left to no enemy units. Victory is yours!
Taking the Center
Some time back, the Battle Report in White Dwarf featured Black Templars and Swordwind Eldar. The Templar player made a comment about using the tactic of "Taking the Center." He didn't explain it very well, but I think I've finally worked out what he meant. The concept of Taking the Center involves crossing the opponent's "T" and cutting off part of the enemy army. Essentially, you are driving a big wedge through the middle of the enemy army. In doing so, you are attempting to isolate one side from the other, preventing them from being reinforced from the other side. The way you do this will vary with your army and units. You may be blocking Line of Sight, or using sacrifice units that will slow down the enemy on the outside. Some of this can also be achieved by the means of "Dividing by fire." This concept uses concentrated firepower to wipe out enemy units closest to the area you are intending to effect, increasing the distance to any relief units the enemy might bring to bear. Ultimately, how you project your power is up to you, but project it all at once, committing piecemeal is a great way to get your army wiped out with no effect.
Once you have one side cut off from the other, the bulk of your army is concentrating on the half of the enemy that you have trapped. Concentrate firepower or assaults or both against the units you have trapped, but make sure that you have everything ready to go once you spring your trap. If you don't defeat the trapped portion quickly, then all of your units will quickly be entangled by the enemy and it'll be their whole army against yours, which are not the odds we're looking for.
Once you have defeated the trapped units, you then turn to the other half of the enemy army. By concentrating most of your army against only half of the enemy army, you should have more than half of yours left. This means you'll be fighting at an advantage here, which should give you the win.
The Oblique Line
This is a tactic to counter the usual linear placement people use when they set their army up across the length of the board. The idea is to concentrate your fastest movers and heaviest hitters almost entirely on one end, preferably not against the enemy's best units. It can be useful to leave one of your tougher units on the far end as well, but you'll have to experiment and see which you prefer.
As your army advances or you project your firepower, allow your heavy side to move ahead of the rest, with the middle advancing faster than the far side.
When your heavy side hits the enemy line first (or your firepower starts eating into them) it should wipe out or break the opposing enemy units fairly quickly. Ideally, they should finish about the time your center units show up. Now the units in the enemy center start coming under attack from both your heavy side and your center units at the same time. This is known as rolling up the enemy flank.
These should crumble quickly from the attention and fall just in time for your far side to hit the enemy lines, allowing you to continue attacking at an advantage.