First, your army should have a theme. It should not be a jumbled mishmash of different Chaos Squads, a themed army will be both a better fighting force and more enjoyable to game with. The reason I outlined the different Traitor Legions was to show you the different themes that you could give to your army.
I prefer the theme Chaos Undivided. My interpretation of this is not to just use a mix of all Chaos types, but instead to build a well-balanced force with the special types in a supporting role. For my Chaos Undivided force, I use mostly standard Chaos Marine types, with small units of Plague Marines and Noise Marines as support. I use Veterans in a scouting and flanking role, and I use Terminators as spearhead troops, supported by Tacticals and Devatators. I sometimes, but not always, use a unit of Khorne Berzerkers to break and/or disrupt my opponent's line. I use crossfires and killing zones to cut down my enemy's strength before making assaults. You should concentrate your firepower just as you would with a normal Space Marine army.
An Assault Army
With this type of army, I go heavy on the Khorne Berzerkers, including Terminators. With this army, it is imperative that you close with the enemy quickly, and that you concentrate on one area of his line, because you will probably be badly outnumbered. Attack and destroy your enemy's line in detail, concentrating on one area at a time. Use speed, and do not allow yourself to become bogged down.
A Thousand Sons Style Force
This is for the player who likes to use a lot of psychic abilities. The Thousand Sons Marines have good psychic saves and immunity to psychology, but they have a weakness to Force weapons and to the Energy Drain card, so take this into account.
The Death Guard
Plague Marine armies have good Toughness, blight grenades, and their plague knives. I look at these as basically assault troops, though they are probably closer to Tactical troops. They make for a fairly balanced, if exspensive, force.
When you are fighting against Space Marines, you should use your ability to have an abundance of heavy weapons and special weapons to your advantage. You and the Space Marines will both have Power Armour and Rapid Fire, so you must use the fact that all your troops can carry assault weapons and the fact that you can generally have more heavy weapons to give yourself an advantage. Also, loyal Space Marines have nothing that can compare with your Berzerkers, or Veteran Chaos Marines' infiltrating ability, so use these to gain an advantage. In my opinion, Chaos Terminators have an edge over the loyal Marines' Terminators, I believe that the twin bolter is a better weapon than the storm bolter, it always gives you two shots and no chance of jamming. Also, you can Mark your Terminators as Berzerkers, or Plague Marines. Also, you can set up Terminator Devastator squads, something normal Space Marines cannot do, which also can be used to advantage.
When fighting Orks, you will be outnumbered, so you must concentrate on one area of the Ork line at a time while delaying other areas from getting to the battle. Nurglings are great for this. You have more firepower and better armour and this must be used to full advantage through the use of Rapid Fire to win against the horde of greenskins.
When fighting Eldar, you have the same problems as you do against Orks with the Eldar's added speed to also have to be overcome. You must nullify the Eldar's speed advantage, and a good way to fo this is thru the use of overwatch fire. You will not be as badly outnumbered against Eldar, but you will still probably be outnumbered. The Eldar's strength is in their maneuverability and speed. Some of this can be nullified through the use of infiltrating Veterans. You can also use a large number of heavy bolters and autocannons to aid in dealing with Eldar.
IG: You fight IG exactly as you would Orks, except you need heavier weapons like lascannons to take on the IG's heavy tanks. Again, you will probably be outnumbered, so you must concentrate your firepower and your assaults on one area of the enemy line at a time.
Bugs (Tyranids): Use lots of template weapons and sustained fire weapons. Cut down as many as you can before they can close with you.The Bugs' strength is in close assault, so deny them that strength by the use of firepower. Take flamers and heavy flamers for use against Tyranid hidden troops, and purchase bionic eyes and scanners for characters to use to detect Lictors.
I do not advocate using large numbers of Daemons that have to be summoned. I believe the points are better spent buying Chaos Marines and equipment for them. That is my personal preference, but I have found my methods to be successful over the years and I have invariably won over armies that were heavy on Daemons. The Chaos Space Marines are in my opinion some of the best troops available. They are much better when used as a Legion than they are as an odd mix of troops and Daemons. They are much better at the combined arms role than the average army. They are only surpassed in the variey of troops and in flexibility by the Orks, and possibly Eldar, but then they have their own strengths that the Orks and Eldar do not have, which you must use to your advantage while minimizing the weaknesses, mainly lack of numbers, that the Chaos Marines have.
Now it's time to call forth your Chaos Legion and go forth and destroy the weak Imperium of the weak Emperor!