One of the biggest complaints among players of Champions Online is the strong focus on the solo element of the gameplay, along with the difficulty--or lack thereof. These concerns aren't unfounded, as the majority of the game's main content can be completed pretty easily without the aid of a team. That said, the social and teaming aspects of the game are there for people who wish to take advantage of them and like a bit of a challenge; it's just a matter of taking the initiative and using those features.
The core of effective team play in CO are the Builds and Roles system. With this, you can customize your role in a team and tailor your hero to your immediate needs.
The four Combat Roles in Champions Online are Avenger (Offensive Focus), Protector (Defensive Focus), Sentinel (Support Focus), and Guardian (Balanced/Standard). Each one modifies the effectiveness of their respective power types. Damage-dealing powers are boosted while in the Avenger role, the Protector role improves your defensive powers, and so on. While in Guardian, your powers all perform on their standard levels.
You can find a rundown for how each role is set up on the Champions Online Wiki.
Effective use of roles within builds can maximize your effectiveness in a team, so make sure you pay attention to which powers will be affected by a certain role, and configure your builds accordingly.
A "build" consists of: active powers, equipment and devices, a passive power, a costume, and finally a role, which is the core of the build. The equipment you use in a given build should complement the role for maximum effectiveness. Your main stats, or Characteristics, (Strength, Dexterity, Constitution, Presence, Ego, Endurance, Intelligence, and Recovery) are modified in real-time by what you have equipped. Sometimes these changes can be drastic, so it's best to pay close attention to them in relation to your role. By matching your equipment with your role, you can be that much more effective and make the most of it.
For instance, if you're in the Avenger (Offensive) role, your damage output is increased by 20% before your equipment is factored in. If you then use Offense Equipment that boosts your Strength Characteristic on top of the Avenger modifications, then you'll be even more effective in dealing damage. That kind of configuration in a well-structured team brings an entirely new feel to the combat of the game. Rather than being entirely self-sufficient, you begin to rely on the skills and abilities of your teammates.
So now you know how to build an effective team. What do you do with it? Of course, using a role-based team isn't too practical for open-world missions, or even standard mission instances. There is, however, content in CO that is geared for just that--role-based teaming. Here are a couple of examples:
The villain strongholds are five-man instances built specifically for teams. Here's where effective builds and role usage comes into play. When members of a team take full advantage of their respective roles, you'll find that the combat and team mechanics can really shine. Having an entire team play in the Guardian (Balanced) role might be more effective for finishing content quickly, but for those people looking for a dynamic experience different from the standard solo play in the game, taking advantage of roles in a team and full usage of different power types can result in having a much more fun experience playing as your hero.
There are also the team-based PvP instances. These matches take a considerable amount of synergy when using role-based teams. While they can seem difficult at first, if you gather some friends and practice in your respective roles for a bit, it's not impossible to get the hang of. Personally, I've found myself to be more effective when I can focus on my role and let my teammates handle theirs.
People wanting to tank in a team should make use of the Protector role, for boosted defense and threat generation. That means making yourself the target in a group of enemies, and keeping their attention while your fellow heroes take them down. Constitution and Presence are the important Characteristics here.
For damage dealers, the Avenger role is ideal. Equipment that boosts Strength and Dexterity is a key factor. It's a good idea not to stray too far from support and tank characters--not only are your HP lowered, but so are your self-healing capabilities and your hold/knockback resistance.
The idea of a support character isn't always a very popular one, nor is it common in the realm of superheroes. However, unlike most other games, CO's structure allows you to pick and choose any powers you want, allowing you to have support powers without focusing your character on that aspect. Also, there's the new Celestial set, which offers dual-function powers. If you're targeting an enemy, the power will act as a debuff; if you target an ally, it'll have buffing effects. This works great, allowing you to be a fully functioning support-based character without spending your entire career on the sidelines of the action.
While this isn't at all a comprehensive guide to teaming, it serves to get the ball rolling for people interested in teaming, yet are either uninformed or confused about the use of builds and roles, and how that relates to teaming. I'll be the first to admit that there could be a stronger focus on teaming in Champions, and I hope it will come in time. But for now, what's there isn't bad. It's rare for core game mechanics to be built around shaping how a team works; normally that's handled by developing content simply too hard for one person. In this case, Cryptic has worked the teaming aspect from a different angle--shaping not only the mechanics, but our characters themselves, around how we want to build our team and tackle challenges.