First off, a unit deploying by Deep Strike enters the game from reserve. This means you have to roll dice to see when (or if) they show up to the fight. Special circumstances and rules aside, your deepstrikers will not be present at the beginning of the game.

They generally won't arrive till about mid-game, and may not arrive at all if you keep rolling 1's (hey, I've seen it happen). This can be a potential problem if the unit represents a large points investment on your part, because they won't be lending their weight to the battle for a while.
 

Another drawback is the fact that you often cannot choose their exact position when they arrive. The rules dictate that you place a model from the deepstriking unit and then roll for scatter. They could potentially land up to 12" from where you need them to be. If the dice are really unkind and your unit scatters on top of the enemy (or off the table!), your deepstrikers are history. That's right, they're gone! Do NOT pass go. Do NOT collect 200 dollars.

One final drawback is that, when they land, they are all clumped up and cannot move or assault. These guys better be able to lay down some impressive firepower or be in a protected spot (preferably both). Why you ask? Can you say Ordnance Template, boys and girls? I knew you could.

Now that I've gone over the pitfalls of Deep Strike, here are some advantages:

Rapid-Response: Deepstrikers can make a great "save your bacon" unit. Wherever you may be having trouble during a game, the deepstrikers can be dropped in to help reinforce your line. I've seen a Deep Striking unit turn the tide of a game. It's a gamble, but it's really gratifying when it pays off.

Pest Control: That Basilisk behind the hill giving you problems? Drop some guys in there to blow it sky high. Problem fixed. Deepstrikers are great at getting to areas of the battlefield that the rest of your force may have trouble reaching. This duty is best performed by a unit with firepower, or the pest will just turn around and blast the crap out of them in your opponent's turn.

Capturing Objectives: Deepstrikers are notoriously fickle about when they decide to join the fight. If they decide to show up late, they may not be able to kill enough stuff to justify their expense. They can still grab points for you by grabbing objectives. When they arrive from reserve, deepstriking units are at full strength. Depending on the situation, it can sometimes take a bit of effort to get a unit below scoring level. Dropping a unit on an objective late in the game can be a method to capture or contest objectives. A method your opponent may not be able to do much about.

I won't go into the specifics of using Drop Pods right now. Suffice to say they can be used to mitigate some of the problems of Deep Strike. They don't really fit into the scope of a 'general tactics' article because they 1) are only available to Imperial armies and 2) deserve an article all their own.

Likewise, units with special rules that make their Deepstriking more effective (like Eldar Swooping Hawks or the Necron Monolith) really deserve their own articles. Any tactics regarding units like these will be in the Army Specific Tactics section.
 

I've talked about some of the pros and cons of using Deep Strike. There is quite a range of units in 40k that can use Deep Strike. Some are better than others. Instead of going through each and every unit in the game capable of Deepstriking, I'll go over a few basic types, noting a few examples from various armies that fit the description.
 

These are the big boys with the big toys; monster units, with the price tag to match. They have a good statline and can unload some SERIOUS firepower when they land. Space Marine Terminators and Chaos Obliterators are good examples of "Heavy Hitters". They can be very effective, but they're expensive as hell.

These guys drop in, hose down the enemy with some hefty guns, and are tough enough to be able to soak up some retaliation. If you're using Terminators, a Drop Pod can really boost thier effectiveness (more on them later). A squad like this dropping into your opponent's line can turn the tide of a game. I know, I did this all the time with my Space Wolves.
 

Think of these boys as "one hit wonders". Small, cheap units dropped in to perform a job, then die horribly once it's done. A good example of a "Suicide Squad" would be Imperial Guard Veterans with the Drop Troop doctrine, armed with plasma or melta weapons. Their primary targets will be enemy vehicles, though a plasma armed squad can put some serious hurt on enemy infantry.

These are 'high risk, high return' units. They will often be landing close to the enemy, so the risk of losing them on the drop is very real. They're pretty cheap, so if they die without doing much it's not a huge loss. However, since they're so cheap and often pack really good guns, they are ideal for 'Pest Control'. Just don't expect them to survive for long.
 

These are units that can dish out just as much damage as a "Heavy Hitter" unit, but don't have quite the same ability to take the return fire. Tau Battlesuits are just such a unit. The amount of firepower they can throw down is impressive, but any concetrated return fire (or, god help you, an assault!) is likely to hurt... BAD!

"Glass Sledgehammers" are best used to support your line in a 'Rapid Response' role, reinforcing weak points or helping to bail you out of trouble. Risking them on 'Pest Control' duty should be a last resort. They're far too expensive to just throw away like a "Suicide Squad."
 

Just because a unit can Deep Strike, doesn't neccessarily mean that they should. Some units have the ability, but really don't have the equipment or statline to make the most of it.

Look at Space Marine Assault Squads, for example. They have the ability to Deep Strike, but very few special weapon options to make a decent show of shooting on the turn they land. They are also expensive and will be all bunched up if they Deep Strike, ripe for an ordnance shot. The alternative is much better; deploy them normally and use their Jump Packs to make them a threat from the beginning of the game.
 

In the best case scenario using Deep Strike, Assault Marines might be ready to do something by mid-game. They're still in reserve on turn 1, and won't be able move or assault if they show up on turn 2. So starting on turn 3, they'll be able to perform at full effectiveness. The same is true for any other assault-based unit that uses Deep Strike. For these types of units, the only instance where Deep Strike should be used is when the alternative is certain death.

Picture this: You're stuck on the 'sparse' side of the table, with little or no terrain, looking at a good 2-3 turns of walking into the 'business end' of your opponent's guns. Suddenly, taking a chance dropping your troops behind the woods in your opponent's deployment zone looks like a really good idea!
 

Deep Strike can be effective, but tricky to pull off. Before deciding whether or not to use it, you must first determine: What kind of player are you? Do you like to gamble or play it safe?

If you're a gambler, then Deep Strike may be your thing. There are entire armies that use Deep Strike as their theme, Imperial Guard Droop Troops and Drop Pod Marines to name two. These armies are for players who like to take risks. They can be very powerful, having masses of gun toting soldiers dropping from the sky can rattle even the most seasoned of players. They can also lose horribly because you are largely at the mercy of the "Dice Gods".

If you're the type of player who hugs cover when you should really go for the throat, then deepstriking troops might take you too far out of your 'comfort zone', and that can lead to mistakes. Mistakes with Deep Strike tend to cost you big!

My advice is to try it out. See if it works for you. I have used it to great effect with my Space Wolves, not so much with my Tau. It really depends on the effectiveness of the Deepstriking unit and how they fit into your overall plan. My Space Wolves are a very "go for the throat" army, so Terminators hurtling into battle in a Drop Pod suited them well.
 

Well that about does it for the 'Special Rules'. I'll get around to some of the other rules based tactics in the fairly near future. I've got some thoughts on Hit & Run and Scouts, but I've got to get them straight in my brain before I put anything into writing.

Now I think it's time to look at some specific armies of the 40k universe...