One of the things that annoys me is when writers assume that the bigger the sword the more effective it is. This simply isn't true and a writer concerned about realistically portraying sword fights should realize this. Swords are for cutting (and less often for thrusting) not for crushing so weight is meaningless. A heavy claymore or bastard sword is more likely to merely tire the user and isn't more necessarily more effective. In sword fighting, agility and maneuverability count.
Smaller, lighter swords are generally more maneuverable. However, a very light weapon (epee type) are so light that it would be difficult, if not impossible, to parry a heavy weapon with one. It would give way under the pressure.
Smart sword fighters don't jump into the air. It may sound cool, but it would get the fighter killed. The fighter can't change directions mid-air and doesn't have any way to maintain their balance. A sword fighter's feet belong on the ground in a sword fight.
All parts of the sword are a weapon, including the hilt; so are insults or a face full of sand. Especially with a larger opponent, legs are great targets. A fighter can win simply by letting an opponent bleed out after a leg slash. Eye-witness accounts indicate this was a frequently used technique.
A sword fighter should be closely aware of their opponent. An opponent's hands and shoulders often tense momentarily when they are about to strike, for instance. They may glance the direction their going to move. A fighter needs to also be aware of their surroundings. Sending an opponent backwards over an obstacle is always a good thing.
Last, but not least, a fight to the death takes tremendous energy. A good fighter doesn't waste it on fancy maneuvers that may look cool but don't damage their opponent.
On writing about sword fights a few well-known sword fighting terms are good to use, I think, but I'd suggest not going over-board. There are extensive terms for the Italian and German schools of fighting and somewhat fewer for English, but they would merely confuse the reader. However, block, dodge, parry, and riposte are terms that are familiar and give a picture of the action to the reader.
A fight to the death is serious business. While the Wesley vs. Inigo Montoya sword fight in the Princess Bride was hilarious, it was a great example of how to write one that surely no one believes or takes seriously. I could mention others that were meant to be taken seriously but don't want to offend the fans of some good writers whose sword fights make me cringe.
You don't have to be an expert to write good sword fights. I do think it helps, though, if you get an accurate reproduction and try it out at least, even if you don't have the time or desire to be in a club. If you take some of this into consideration, your sword fight scenes will have a lot more believability.