If you ever want to hit up duel server I'll show you a few tricks - and anybody else in there as well. You'll get the hang of it with practice. Its hard to articulate what you need to do with footwork and positioning, but which direction you choose to attack with is definitely important, and left swing will be your quickest attack.
If you're too focused on the act of attacking alone, you're losing track of them side stepping you, so you gotta refocus your camera when you get a chance to focus on or near the target. You'll find with practice that you actually have a great deal of time while people are planning their attack strategies in a duel.
One thing to look for - They'll attack first - you block - then you get a swing ready, they'll either:
1) Get a block ready. If they get a block ready, hold your swing - you have the upper hand and do not need to swing immediately. Hold it for a second or two. You then have a chance to get a good position and wait for a weak spot in their defense. If they only tapped their block, or blocked the wrong direction, then you release and get a free hit on them, not to mention there's a damage bonus for a held swing as opposed to a quick lash. If they held their block and successfully defended themselves, then neither of you are hurt, and you start over.
2) They might immediately go for a second swing. Its possible to outswing them if your timing was perfect, was a left swing, and you move slightly out of the direction of their swing. If you aren't confident in your swing though, cancel with a block immediately, and play safe. All you need to do to survive is hold your shield up in a 1 on 1 situation. Experiment with shield speeds too, as elite cavalry shields and heavy round shields will play much differently than a heavy board shield or huscarl.
In a heavy melee situation, you'll want to face forward and play safe, but when assisting a teammate or seperated from the pack and can afford to play offensively, your main objective is going to be to get around your enemy. If they do a right swing and you step left, you're essentially doubling his speed by walking into it - imagine a car in oncoming traffic. If you step to your right, or with his swing, and you did a left swing, you're negating his weapon speed, and increasing yours. Overheads and thrusts are tricky, but a 1 hand overhead is the biggest damage output and is still really quick, but harder to aim. Right swings are your best bet for getting the most out of your weapon's reach, especially if you've got a long weapon like an Arabian Cavalry Sword. When you get better at the game, you'll find yourself fighting near your weapon's max range, but don't focus on that too much yet.
Practice makes perfect - you'll get the hang of the game mechanics just by playing. Stick with it.