If you’ve got a local renaissance fair, your best bet would be to actually find the people using swords and seeing what they’d be willing to teach you. Most of the renfair participants I’ve known, have been more than happy to explain what they know.
There’s that old cliche about writing what you know, but if you can get hands on experience, it’ll go a lot further than anything I can offer you.
Beyond that, I’d recommend spending a little time familiarizing yourself with German school fencing.
The general idea with German School fencing is to maximize the efficiency of blade movement. Most guards are kept across the body, to aid with parrying. Most hews (strikes) focus on very narrow blade arcs.
For an experienced fighter, their blade will feel like a natural extension of the arm. I know it sounds corny, but it’s also true. They’ll know exactly where the blade is at all times. The weight and balance of the weapon will have been completely internalized, to the point where they’re probably not even actively aware of them anymore. If they’ve trained on multiple blades (which is very likely), then they should be able to acclimate to a new sword fairly quickly (which is usually what those test swings you’ll see in fiction are for).
Obviously, there’s a bit more difference if you’re moving from a shortsword to a longsword or from a saber to a claymore, but so long as your character is using a sword that’s similar to the one they’re familiar with, acclimation should be fairly easy.
Also, it’s worth pointing out, German School fencing is specifically intended for European longswords, you can use an arming sword, Viking sword or bastard sword, but it won’t be a perfect fit. Additionally if your character is using something like a scimitar or a greatsword, those all encompass different styles.
Ironically, the original Star Wars trilogy isn’t a bad visual reference for German school fencing. There’s more blade on blade combat then you’d like in a real combat scenario, but a lot of the techniques and stances are there.
Michi would be irked if I didn’t recommend the Errol Flynn films as visual references. Just keep in mind that the actors are fighting very conservatively, because they’d been given live blades, and, for the most part, are trained in Italian School fencing, which evolved to use lighter blades.
If you’re talking about using swords in mass combat, as opposed to dueling, then I’d be tempted to suggest Aragorn and Boromir from the Peter Jackson Lord of the Rings films. I’m not as familiar with mass combat forms, but what they’re doing looks close to what I’d expect.
I keep saying this, but look at Robert E. Howard’s Conan. One of the necessary parts of being a writer is finding someone else who went before you and seeing what they did. When it comes to sword combat, and accessibility, Robert E. Howard is probably the best source I can suggest. There’s a fairly cheap three volume paperback set that’s in print, and, because it’s public domain, most of it is available through Project Gutenberg.