Time to start thinking strategy. Chaos Marines are going to be the foundation for these strategies, but many of the same principles can be applied to other armies. The options you have grow dramatically when you start to factor in allies, but I am going to just be talking about Chaos Marines on their own.
Here are some of the main types of armies that you are likely to encounter. Many armies (most of the good ones anyway) will include more than one of these strategies.
Deathstars: While large squads of paladins and biker nobz have generally fallen out of favor deathstars are not dead. Tau and their supplement bring the notorious Farsight bomb and Eldar have jetbike councils. Both can stack multiple USR's making them both durable and able to put out the hurt.
Trying to defend against a deathstar can be tricky since they tend to do a ton of damage in a single turn; you are going to need to prioritize what lives. If I know a Farsight bomb is going to drop I want to make sure things like obliterators or vindicators are either bubble wrapped with a throwaway squad or hiding in reserves.
With both Farsight bombs and Jetbike councils positioning is key. Most often there is one model with a reliable save meant to tank most of the incoming shots. These are both fast opponents so it may be difficult to outmaneuver them, but it is possible.
Throwaway units such as cultists and Typhus zombies are great for bubble wrapping. If you can manage to catch a deathstar off guard zombies can tie up units in close combat for a significant period of time.
Everyone loves Helldrakes. Baleflamers can make quick work of any squad without a 2+ save. They can also reliably move into a position to avoid a 2+ save tank. It is also important to remember that vector strikes do random wound allocation meaning that it is unlikely that the tanking model will be hit.
Noise marines are also incredible for dealing with these kinds of threats; however, you need to make sure that you have a range advantage on your opponent. Most shooting deathstars have medium to short range on their guns and if you can keep a squad of cultists in between you and your opponent this can really limit the amount of damage that you take. Positioning can be an issue if there is a 2+ save at the front of the squad. Make sure your opponent takes the bolter saves before the blastmaster saves if there is a tank.
Turn Two Charges:
Armies that can pull off a turn two charge are rising in popularity. Swarms of Flesh Hounds can be seen at many a tournament, Wraithwing still makes appearances, and with the (suspected) rise of white scars you are likely to encounter someone who can be in your face on turn two.
How you react to an extremely fast opponent is going to depend on how his or her units are approaching you. If they are running right up the center then it is going to be easy to concentrate your firepower and/or charges on a single unit. However, if an opponent is smart and hitting your flank then you are going to need to react in a more precise manner. Hitting you on a flank means that they can engage only part of your army. You want to move in such a way where your opponent will be forced to engage as much of your army as possible. Against an army that has turn two chargers you are going to want to keep most of your army together. Spacing out will let these fast units pick off your squads one at a time.
Once again bubble wrapping is going to come in handy. Cultists and zombies come to mind; however, I have also had a couple occasions where I was able to bubble wrap with my helldrakes. With some planning and a decent amount of luck you can get this tactic to work and it can be devastating to your opponent. I have only been able to pull this off when I go first simply because it relies on your helldrakes coming in at the beginning of turn 2. When your helldrakes come on the board position them in such a way where your opponent would be unable to charge without place a model within 1 inch of one of your bases. This can force them to be stuck out in the open for an additional turn.
The most effective shooting unit against wraiths, flesh hounds, and bikes has to be noise marines. Against both flesh hounds and wraiths S8 is devastating and bikes will simply melt away against a blast master.
Daemon Princes with a black mace can be very effective against these units in close combat. They are fast enough to engage these units and pack enough punch to do some serious damage. Since they don't have the 'Champion of Chaos' special rule they do not actually have to challenge (however they more than likely will want to).
Baleflamers are ok against flesh hounds and wraiths since the STR wont double out their toughness, but the Hades autocannons are very effective. Bike squads cry at the sight of a baleflamer.
I have not run one but on paper a forgefiend with two hades autocannons and a single exctoplasma cannon would be effective as well.
