First off, try your hardest to not play bruiser. Its not a bad mech, its just not in the top half of good mechs. Its hard to play, because the Hellfires are underpowered. I'm going to keep screaming this until they get buffed. They won't get buffed, and I'm going to go hoarse.
Roles of the Bruiser:
1) Spearhead. First one in, and often first to die. Your job is to push a point with a team behind you and eat as many shots with DA as possible. You can use the Hellfires to flush enemies out of cover, or to shove them behind it. Often you will go in after you defeat one of the opponent's mechs, giving you a numbers advantage.
2) Suppression/Defense. You're behind your spearhead keeping people from shooting at him or her by forcing them into cover. Its almost reflex to dodge behind cover when you hear the lock on sound mixed with a thousand bullets hitting the ground around them. Teamed up with an indirect fire mech, you can destroy people without them even getting a shot off. Additionally, people will hate to try and push against you if you're standing on a point.
3) Support. This role is heavy on the hellfires. Fire the hellfires on cooldown, lock if there is a target available. You won't get many kills in this role, but you'll help others on the team get them. Hellfires isn't huge damage, but its damage that goes around corners and chases people around. If you're buddied up with a spearhead or a fighter mech (Brawler, vanguard, scout, assualt, etc), you can lay out consistent damage while the enemy tries to kill your spearhead or fighter. In addition, if you're teamed up with a sniper, you can flank and flush enemies out into the range of your snipers.
Ok, lets look at the most unique part of the bruiser. Its ability.
DAMAGE ABSORB: Reduces the amount of damage your mech takes for a short duration. Damage Absorb has a 16 second cooldown.
Honestly, this is one of two reasons I play bruiser. This ability is ridiculously tight. It takes a bit of skill, situational awareness (game sense), knowing the enemies tempo, and a little bit of hearing. I want to say Its somewhere in the realm of 65% damage reduction for 1.5 seconds. Throw a Deflector on there and now you're cooking with bulletproof fire. More on internals later.
Knowing when to use damage absorb is what separates the good bruiser pilots from the bad ones. Many of the free week bruisers I see just hit DA at the beginning of a fight, which is not how it should be used. It should be used ideally right after the enemy fires their secondary weapon as a "parry" of sorts. I mentioned tempo, which is a huge part of this. Eventually, you can time your ability as your opponent is clicking to fire, once you learn their tempo. Every player has this. Some players have a slower tempo than others, and its generally faster from A classes. I can't teach this to you, its a skill you need to learn yourself. More on tempo later.
Weapons! (I wish SA hawkins was on this list, but i need to shut up about it because vana told me to)
Vulcan! This is my personal choice, because I can't aim. Also it does immense damage. Its advertised as a point blank weapon, but I've had a lot of luck from RNGesus with it at mid, and occasionally long ranges. Most Importantly, it effectively covers the Hellfire's downside: close range combat. Just hold Mouse 1 and let the bullets do the talking. As long as you can keep the reticule trained on the target, they will die. Again, aiming is not a skill I can teach you.
When to use: On maps where you can keep the enemies in the sweet spot between vulcan effectiveness and hellfire tracking. If your target is smaller than the reticule, they're out of the sweet spot. You want them about where their torso is contained within the reticule. Specific maps: Origin, Uptown, Wreckage. There are area's in the other maps that you can use to keep the enemy in the sweet spot, but overall it will be hard.
Roles: Spearhead, Suppression/Defense.
Submachine Cannon! I hate this weapon, but only because I don't like things that are easy to use. Very fast rounds per minute, long overheat time, and a good amount of damage at short and mid range. Very easy to use, low spread, and good damage. It does however make you weaker than if you had a vulcan if people get up in your grill (literally, Hiefram has a grill) Most good players will get in your grill. Especially scouts. I'm looking at you Omeganull.
When to use: On maps that are heavy on mid ranges. To an extent, you can keep people a but further away with the Submachine cannon, but if they close the distance you can find yourself in a pickle. Specific maps: All of them. The SMC is really strong.
Roles: Spearhead, Suppression/defense, Support.
Assault Rifle! This weapon has really grown on me as a Mid to long range fight stick. Where the SMC and the PD Vulcan fall short (literally) the AR shines. I use this in objective modes where I can keep the enemies at bay with the help of my team. However, If you're a DM or TDM player, Stick with the PD vulcan or the SMC.
When to use: On objective modes with long distances to cover. Siege (anti-air coverage) on Origin, Last eco, Frontine. If you're an EU runner, use SMC or the PD Vulcan.
Roles: Suppression/Defense, Support.
You may be thinking at this point, "No! Thats not what those weapons are for!" I'm considering them with the specific roles of the bruiser. If you want to kill dudes, use Fighting mechs. Moving on.
Hellfires! Man look at them. THEY'RE SO COOL LOOKING. The in game menu describes them as "High burst damage, target seeking functionalily, effective at variable ranges" In this way, Adhesive is playing two truths and a lie with us. Take a guess at the lie! Do it. Ok. (The lie is the burst damage) Just about every other secondary weapon does more damage than the hellfires. Its a sad truth, and they're a bit lower than I think they have to be, but we're trading high damage for the ability to scare dudes into cover. Also they're fairly effective a long ranges, but at that point you should be playing Sharpshooter. I've yelled about various buffs to them (such as a change in functionality, or a damage increase) But that isn't the point of this thread.
Here is where tempo comes back into play. If you've learned your opponents tempo, you'll know when to fire your HFM. A type mechs can be somewhat squirrely with the Hellfires, often having multiple opportunities to use their dodges to avoid hellfires. ALWAYS FIRE AFTER YOUR OPPONENT HAS DODGED. In Duels, your hellfires are a lot less reliable if you don't know how to use them.
Air combat also messes with the Hellfires, making them immensely hard to hit. Often times opponents flying will move outside of the HFM targeting range, causing them to lose purpose and drift into the distance. Berserkers are going to be your main problem here. Just keep your primary weapon trained on them, and try to parry one of their TOW blasts with a DA.
One of my favorite things to do with hellfires is to force Sharpshooters from their crow's nests. This can buy you a few crucial seconds to move into position or pass a point thats being overlooked by a sharpshooter.
Hellfires are also good at slamming someone and forcing them to back to repair. If its a duel, you can Boost>jump>fly over them and catch them with their pants down, blasting them with a free lock and huge amounts of bullets. Its worth noting that the Bruiser has the second highest flight speed in the game, at "34" (for reference, berserker has "42")
To make the most out of your hellfires, you're going to have to learn how to arch shoot them. Depending on where you are on the map, what obstacles are in the way, and which way the opponent is moving, you'll have to arch shoot your HFM after locking. This is a hard thing to teach, but learning how to do it will net you far more Hellfire hits. Usually, you want to fire 60 to 70 degrees to the side opposite of their cover, so that if they dash behind it, your HFM have more room to maneuver behind the cover and hit them. If your target runs behind a hill, you can fire upward to lob them over. This is incredibly useful on open maps, such as Bunker, or Last eco. Say you're fighting around a pillar. If you get a lock, fire to one direction, you can dash the other direction, so that your opponent has to either dash out into the hellfires, or into your Primary weapon fire. It takes practice, but know that you can arch your shots. You have to in order to keep all your damage from flying into a wall.
Heads up: People will hate you. A lot. Arguably as much as a Sharpshooter. You'll hear the words "skillfire" thrown around a lot. Use that. The HFM are a psychological weapon, so if you get your Opponent riled up, they'll play less effectively.
BUG: Occasionally one out of the six, or five out of the six rockets will fail to lock onto the enemy. Adhesive knows about it, they don't know how to fix it yet. Its completely RNG, so sometimes it will happen to you 10 times in a match, or it wont happen at all in a day.
As for internals, the Only Mandatory one is Deflectors. On my main bruiser, I use Fuel Converter and Armor fusor in addition to Deflectors so that I can fly around, collect assists, and generally be a tanky jerk. (72 armor after a kill over 20 seconds is nothing to sneeze at, if effectively brings your armor up to 627 after a kill, and 591 after an assist)
Since you're going to be in the air a lot, another good choice is the air compressor. It helps to reposition yourself in order to land more hellfires, however it takes a bit more awareness and APM (actions per minute) to pull off.
There are no mandatory items, and you can change them around to how you want to play. I like HE charge or Detonator for huge alpha strikes.
NOW! There is only so much you can learn by reading. GO FORTH AND INCITE RAGE MY MINIONS