In general, everyone on your team needs to play as a light with a Carb-9. Especially on offense. Competition is all about doing the objectives fast and having even one medium or heavy on offensive with slow down your entire team a great deal. On defense you can get away with running a medium with a longer range rifle on some maps. The Carb-9 sucks bawls at anything beyond about 20ft, but almost all of the fights in Brink take place within its effective range and no other gun comes close in effectiveness. The extra health of medium and heavy is pretty much useless. A light with a Carb-9 can take down a heavy in a straight up firefight unless the heavy is shooting them at point blank range with a shotgun.
On defense the two most important keys are knowing where the enemy is and being able to re-position your team dynamically to counter that.
On each object you’ll want to establish (in advance) a particular zone of control that your team plays within. For example, on first objective Aquarium it is very effective to control the red and blue rooms as there are only three possible entrances (red, top, and blue). As long as you have control over this zone the enemy cannot win.
Identify the paths that the enemy can take to get into that zone and ensure that you always have at least one pair of eyes on that pathway. Obviously the fewer choke points you can create the better. This is critical in choosing the zone you will control. The sooner your team identifies the paths the enemy is taking the more effectively you can counter them. When the enemy is weakened, push out slightly so that you can see more of the map. As soon as you identify the direction the enemy is headed, fall back into your zone and set up to intercept them.
Once you identify the entrances that the enemy is planning to take your team needs to re-position itself so that you are guarding those entrances more heavily and the other entrances less heavily. Remember that the attacker is probably going to hit you with either 2, 3 or 5 guys at once, and a single defender cannot stop that. Thus, your team needs to shift at 3 or 4 guys into the path that the enemy is taking so that you can stop them effectively.
On defense you don’t want to push forward. In most cases, the enemy can’t hope to win while you’re still alive even if you can’t kill them. Play defensively and stay alive even if it means not getting as many kills. You can defend fairly effectively against a team that outshoots you to some degree.
Watch your spawn times. Defense has a long 30 second spawn time, but they are very predictable. If you are very low on health with no medic near then with 5-8 seconds to spawn push out into the enemy and die so that you can catch the next spawn wave. The defensive spawns are so close to the objectives that dying is not a major problem unless you hit a long spawn time.
Abuse mines and turrets. Place mines in doorways, not on top of objectives. Turrets are annoyance weapons, not killing weapons. Place them with line of sight on an objective such that the enemy cannot complete the objective without first killing the turret.
On offensive never travel in groups of less than 2. Don’t attack an enemy unless you have at least two people shooting at the same guy. The defense can afford to die, you can’t. This means that your offensive pushes need to be either 2+3 or 5 man pushes. There are a limited number of effective attacks for any given objective; so plan these in advance. If one side seems weak send a 5 man push to it. If the enemy has an effective hold on both sides try a split attack. It’s helpful to have pre-defined teams. For example, A, B and C always travel in a team of three and D and E always travel together. Then when you’re improvising you can just assign two attack positions instead of five.
As with defense, time your attacks according to the spawn time. Push in with 5-10 seconds left on the spawn timer. If you die, you will respawn soon at least.
Your attacks need to hit with maximum force as quickly as possible. The longer it takes the 3 or 5 of you to enter a fight the more time the defense has to re-position itself.
Be aware of spawn invulnerability. On some maps (Terminal), the defense can literally walk to the objective while still invincible. If you can’t hurt the enemy, stop shooting them and just wait.
Abuse grenade shooting and soldier grenades in general; nothing is more effective for attacking a camping defender.
To win on offense you need to be able to win firefights. Unless the enemy is dumb, you can’t win while they are alive. Strategies play a much bigger role on defense where winning firefights isn’t as important. On offensive you just need to win fights and not be dumb.