Melee is all about keeping pressure on your opponent. Obviously not everyone will stop shooting at you, so the first thing to learn is throwing off their aim. Jumping and rolling frequently while blocking can close the distance without taking damage. If an opponent has a high capacity weapon and starts to deplete your block gauge too fast, don't feel too bad about backing off to replenish your block gauge and health.
Getting within distance is only half the battle. Against all but the most unwary opponents, you will likely only get two swings in before they leave your range. Two slashes into a forward roll followed by a third slash usually seals the deal. If they cannot be caught by a quick roll, carrying a fairly high damage secondary weapon, like a shotgun or rifle, can drop them as soon as possible.
Carrying two swords will not increase your attack capabilities, save for being able to throw one of your swords. However, it does have it's defensive uses. Each weapon you carry with the capability to block has it's own block gauge. Thus, when you carry an improvised weapon and two swords, you can have up to three block gauges. This is likely enough to drain all but the assault rifles of their clips. Also keep in mind that when blocking with one weapon, your other gauges are regenerating, further extending your ability to block. Use this knowledge to exhaust an opponent of ammo.
Carrying two of the same gun will NOT allow you to use them at the same time. In most cases this makes using two of the same gun fairly pointless. However in the case of the rifle and the RPG, which have single shot clips, you can fire two rounds in quick succession without reloading. In the case of the rifle, this can deal 100% hitscan damage almost instantly. Double RPG shots can keep teams off guard, perhaps even netting a surprise kill or two.
The AR has a large clip but a very long reload time so often players will carry two so that they can stay in combat for much longer without having to reload.