It always amazes me when I run into people who don't know the capabilities or even some of the basic rules of their own army. There's always a period of adjustment when switching from one army to another, but after you've played a few games you should know the basics of how your army handles on the tabletop.

You have an army book. Read it. Cover to cover. Then read it again. It is crucial to know your army inside and out. Have a look at each unit entry in your army book, and think to yourself: What's this unit good at? What's it's job, and more importantly, how does it do that job?

There are several things you want to consider when measuring a unit’s effectiveness.

Deadliness is the unit's ability to dish out damage. By using probability, you can calculate how much damage your units are likely to inflict in a given situation. You can also calculate your opponent’s ability to inflict damage in any given situation. When calculating damage potential, range is also an important consideration. Some units deal damage at range, others only up close. Each type handles very differently on the tabletop.

Resilience is the ability of your unit to take damage, either by resisting it or absorbing it. This can be represented by a good toughness or armor save, like Space Marine Terminators, or by having expendable bodies in the unit, like Orks. Whether or not you plan on the deploying the unit in cover can also be a factor of resilience.

Maneuverability is the ability of a unit to move around the board. In 4th Edition 40k, due the high value of objectives in a mission, maneuverability is just as important as the ability of a unit to dish out damage. A unit that hasn't killed anything the entire game can still be worth a lot of points just by being able to move in and capture an objective at the end of the game.

Having a good balance of these factors, like a unit of Tactical Marines with a Rhino transport, makes for a well rounded unit. Units that sacrifice one ability in favor of another will usually be specialized units. Tau Battlesuits would fall into this category, highly maneuverable and deadly, but pretty fragile. A unit that excels in all areas will be prized units, but you'll pay through the nose for them.

Cost is the price of the unit in points. While not really an aspect of a unit's effectiveness, it is vital in determining a unit's efficiency. There are some units out there that have a good statline and a dizzying array of weapons and options. Units like this can be a real nightmare for your opponent to deal with, but represent a substantial chunk of the armies point total. The big problem with these types of 'super units' is they are generally overpriced for what they do. You can often get several cheaper units for the same price as one expensive unit, and they will often perform just as well, or often better, on the battlefield.

Determining what units to take for any given battelfield role is only one part of the equation. The units in your army need to support one another for maximum effectiveness. I'll cover this in more detail later, but for now let's look at the other aspect of Sun Tzu's philosphy ...
 

You don't need to own every codex for every army in the game (I do, but then, some people say I have a problem). However, it's a good idea to have an idea of what your enemy is capable of. A decent understanding of the enemy army as well as some of the special rules associated with them is critical to knowing how to fight them. For example, if you didn't know about the "We'll be Back" rule of the Necrons, you might be a bit put off when they started getting back up after you killed them.

You use the same balance of deadliness, resilience, manueverability, and cost to gauge the threat level of your opponents units as well. But that's only part of the equation. Just like your own army, you must look at how the units in your opponents army will work together. Remember, the whole is often greater than the sum of it's parts.

Knowing what your enemy is capable of, and how they fight, is the key to beating them. You don't have to tailor your army list to each opponent, in fact it's best not to. What you DO have to do is change your tactics against different opponents. There's an old saying: "If you cook all your food in the same pot, you're not going to like the taste". True words. You can't treat a Tau army the same way you'd treat a Tyranid army. They fight in completely different ways.

This section has been primarily devoted to looking at your army in terms of statlines and rules, essentially concentrating on how to put together a good army list. However, analysis and "math-hammer" will only get you so far. Next we'll look at some tactics and strategy, basically how to put your army to work. Have a look at the next section for some tips and tricks.