A lot of warhammer fantasy talk is about lists, upgrades, magic items, dice rolls... but in my opinion, much of the important player interaction as far as strategy is concerned, happens in the deployment phase. Of course, the movement phase is a big deal as well. Warhammer is a game of position, and sometimes very powerful troops will be made reduntant by flank charges, march blocks, or even choked out of the battle by friendly forces in a bad position.
Let's have a look at this crucial part of the game in detail. I've won and lost some very decisive games on how well or badly I deployed relative to my opponents. When both armies are set up and I see some bad deployments by my opponent, I know it will be an easy game. But if I see myself outsmarted in the deployment phase, I know that it is likely I will lose.
Number of Deployables
I think this is something every player ought to take into consideration. If you have a lot more deployables than your opponent, you can lay down a lot of less significant elements of your army early on, and by the time your main hammer units or vulnerable pieces are ready to be deployed, you will know where the enemy threats are. On the other hand, the 'choice' locations on deployment zone, i.e on hills, between forests.... may lack room for everything you want. It might become more obvious where you are going to deploy your important items, as the relevant space closes up.
How important is getting that +1 to the roll for first turn, for your army? Do you ever make changes to your list just to have more or less deployables? I think one quite advanced warhammer strategy is to count the number of enemy deployables before the game starts, and work out whether you will finish first or second. Try to figure out what your opponent is going to deploy last.
Order of Deployment
I think the general rule of thumb is that you deploy your fastest units first. In an average dark elf army, this might be dark riders and harpies. On the other hand, your slow moving, vulnerable to missile fire units may want to be deployed last. You want these directly opposite whatever they need to engage. If the enemy saves their target to deploy after you've committed them, they've immediately got an advantage.
I've been thinking about this, though. Suppose your style happens to be like mine - very conservative. You might be playing some kind of fragile gunline - high elves with no spearmen, light on infantry, but with eagles, cav, archers, RBT's. You want your long range missile section to be as far away from the enemy as possible. This could mean deploying even your hammer units, elite infantry, etc before your ranged stuff.
Of course the opposite approach serves another strategic purpose. You deploy all the artillery/ranged first. Then while the enemy is gathering up opposite that, you are now in a position to deploy your hammer cav and fast can in such a way that you can immediately move into better angles, flanking positions, march blocks etc.
Deception in Deployment
The deployment phase in warhammer is quite unlike deployment in WH40k. It is call and response - you interact with your opponent in a turn based 'minigame' that is in many ways more strategic than the rest of the game itself. There is NO luck in deployment, no imbalance, no cheese. If you can outsmart your opponent here it is decisive.
Faking a flank deployment is certainly a way to do this. You deploy several units of fast cavalry on the same flank, and your opponent unwisely takes the bait by placing a hydra, or steam tank, or elite infantry unit opposite them. You are now in a position to deploy your entire army on the other flank, and march over to the rest of your army with the fast cav in the first turn. In many cases this trick is not subtle. Good players will not fall for it. But it can be worth trying anyway - if you can keep them guessing about where the main bulk of your army is going to be, for longer, this is good.
Terrain often makes the placement of troops predictable. Big hill smack back in the middle? All of your artillery and ranged is going there. Forest on one flank? Won't see much heavy cav there. But, I think sometimes you can really use this expectation to your advantage. There is no reason ranged units can't be deployed on flat ground even though there is a perfectly good hill nearby. If you can trick your opponent by saving the units expected to appear on a hilltop, until any threats have been placed - you might find that conceding the advantage of the hill is trumped by the advantage of stationing your units in a safer position.
If you can, look at your quarter strip of the table and work out where each unit will go by default before you place ANYTHING. Your plan might change as you see your opponent's units go down. But, like the rest of the game itself, having a plan as well as a willingness to respond to your opponent is very important. If you simply place units in response to your opponent, you might realise later on that the ideal spot for one of your most important units is now taken up by other things. If the zone is choked up with impassable terrain and forests this is more likely to happen. If you have a default spot for them mapped out in your head, you are then in a position to choose between the various areas that are NOT taken up by any of the default spots when it becomes necessary to deploy something in a position that you had not initially planned it to be in.
Those are the main points I can think of for now. Deploying smarter improves your play. I'm sure everyone else has a lot to add and discuss as far as these ideas are concerned, so let's hear it. Essentially this is a much better topic for serious players to be discussing than things like cheese and imbalance in army books. In tournaments with good composition systems, the smartest and most experienced players will come out on top. Let's work towards being more like those guys.