Keeping your preferred dual wielded weapon in your RIGHT HAND:
When dual-wielding, it's tempting to just pick up a second gun and keep moving. However, if you want to truly do yourself a favour, take a moment to consider what your backup weapon is, and how you plan on fighting once you drop your second weapon.
I've seen plenty of skills of dual wielding, and a lot of them show the plasma pistol in the left hand, and the SMG in the right. That's all well and good if you're going to be sticking with the two. However, what if you have to do a sudden melee? Or you want to throw a grenade? Or if the SMG runs out and you don't have time to reload.
If you drop the extra weapon, you've just lost the plasma pistol, and you're stuck with a spent SMG in your right hand. Not very good if you're up against a red Elite, or if you're backing away from a Grey with a sword; you've just dropped the plasma pistol, which he's just walked over... not like you can go pick it up again.
So, keeping this in mind, you think beyond the dual wield. Do you want to alternate plasma pistol/battle rifle once you drop the SMG? Then be sure you keep the plasma pistol in your RIGHT HAND. That way, once you drop the SMG, you still have your plasma pistol handy.
It seems a simple and mundane thing, but it really could mean the difference between surviving a scuffle or having to start again from your last checkpoint. Or worse, giving up that killing blow that breaks the tie in a Live game, to a joker who dropped his SMG in a hurry and had his plasma pistol ready to drop your shields.
Something to think about.