Honestly, if you can, find a better weapon than the SMG. Get a battle rifle or a rocket launcher. Many times however, you will die and respawn with this weapon, depending on the game type. This weapon, in the right hands and a good sense of timing, is deadly.
First I shall deal with the SMG tips dealing with using it by itself, and then in conjunction with other one hand-held weapons. Keep in mind that using an SMG without duel-wielding can be just as, if not more effective than duel-wielding.
Here are tips that will aid you in the heat of battle:
1. You have an extra hand to throw grenades. Use it. Throw a grenade to soften up your target, then move in to empty half your clip into your enemy or melee.
2. Do not underestimate the meleeing power of the SMG. When you are standing still, the melee will take away more than half the target's shield. A running melee will take it down to the point where the enemy's shield is beeping red, and a jumping melee will take away all the shield. If your enemy's shield is already damaged, you will have an easier chance of beating him down.
3. A good way to take out an enemy in close range is to run towards your target, shooting up to nearly fifteen to twenty bullets, then while you're running, melee the enemy. Or you can melee first and then fire. Either way is your choice.
4. Never squeeze the trigger. The SMG has a poor range, making it difficult to defend yourself from a battle rifle or finish off a fleeing enemy. Because of this, pump the trigger; your accuracy will increase, and it will take about a clip to kill your enemy.
Duel-Wielding, as I mentioned before, is not a necessity for the SMG. Many will disagree, but I do have to admit it does have it's advantages. For that, here are my duel-wielding tips.
SMG+SMG: There are two ways you can approach using this combo.
1. Use them simulatenously, pumping your triggers as I mentioned earlier. Though the recoil will be greater, it will still get most of your shots off into your enemy. Two SMGs are in most cases, better than one.
2. Fire off one SMG until you empty the clip. Then finish your target off with the bullets in the other. That way, it will be like having one SMG with twice the amount of bullets. A great way to get assists, actually.
SMG+Plasma Rifle: This is in my opinion, the most powerful combo overall. The plasma rifle will drain your enemy's shields, while the SMG will finish him off. Like the SMG, it is important to pump the trigger with the PR as well to improve accuracy. If the battle is getting intense, and you want to achieve fire superiority, use the brute plasma rifle. Sure in the long run the brute plasma rifle will drain its core, but it fires much faster than a regular plasma rifle. If you have an SMG+Brute Plasma Rifle combo, and your enemy has an SMG+Plasma Rifle combo, you will win, because you will get more shots off. Because of this, replace your PR often.
SMG+Plasma Pistol: This combo is incredibly effective. Charge up the plasma pistol and when you come in contact with the enemy, release the trigger to fire the charged plasma shot to overpower his shields. Then finish him off with not even half of half an SMG clip. But do not rely on this combination all the time unless you're a decent shot, because if you miss that shot, you will become very vulnerable.
SMG+Magnum: The recent autopatch has decreased the stopping power of the magnum pistol's shots, but do not despair. Imagine you have a plasma pistol that cannot fire charged blasts, but has a faster rate of fire, and the bullets reach your enemy's instantaneously, instead of waiting a few milliseconds to reach your target. The SMG will steadily damage the enemy while the magnum will take chunks out of the shield.
SMG+Needler: You may or may not wish to pump the trigger of the needler, depending on how far away your target is. But this combo is quite effective against enemies who are stationary, or targets that are distracted. There are better combos than this one, but do not underestimate it.
I hope these tips have given you a new or improved respect of the Bullet Hose, as it will certainly aid you in many games.