Although written for a cruiser rider who was in a bit over his head with a large bike, these tips apply regardless of bike style or size.
The general rule about cornering at any speed is when in doubt, lean more. A lot of guys think they've entered a corner too fast, panic, straighten up, grab the brakes, or just bail out and crash. Modern tires are really good, and will usually out corner any cruiser bike without sliding, unless there's sand, oil, or other road snot in the way.
My Vulcan will always grind the floorboards and mufflers before I run out of tire, and I'm pretty sure that the Harley's the same.
Start practice with some gentle high-speed curves on a good road with about a 40~50 MPH limit. Enter the curve just a bit under the speed limit, but lean just a bit farther than you think you need to. The bike will try to corner too sharp and cross over the line. Before it gets too close to doing so, keep your lean and give it a bit more gas. The bike will want to straighten up, and your line will straighten back out. Of course you will be cornering a bit faster too. The harder you open the gas, the harder it will try to stand up, and the wider it will want to run through the turn. At that point you have the option to ease off the gas and tighten your line, or lean more and corner harder.
Now do it again, and as you go through the corner and increase the throttle just slightly, and feel the bike straighten up, play with the throttle just a bit. Make very small corrections up and down, and feel your line through the curve change left and right. Also feel the bike rise and fall under you as you tweak the throttle. Get a feel for how much the throttle picks the bike up. This is called steering with the throttle .
As you get better at this, you will be doing the same thing on slower and slower curves, with more and more radical motions. The ultimate goal is to be able to (practically) toss the bike down in a corner until the boards just barely drag, and hoist it back up again as you round the curve by simply using the clutch and throttle.
Be prepared with that clutch and throttle! A split second too late, and you'll be riding on the floorboards completely and the tires will leave the ground! (I did that once on a bike with really big floorboards, and it's noooo fun.) This will come in handy the next time you enter a curve that's tighter than you think. Instead of panic and crash, you'll have the confidence you need to lean the bike all the way, and the practice to control your line through the curve.
You've practiced the bare basics of this at very low speeds in MSF, but the exercises were pretty time-limited. Practice the low-speed stuff some more.
Find a deserted parking lot and take those MSF lessons to their practical extremes. Practice making tighter and tighter circles and eights , and when you feel you're falling press the rear brake a bit and use the throttle. This will hoist you right back up. As the circles get smaller and the speed slower, the motions get too jerky for good control. You'll need to use a (slight) excess of throttle to prevent snatching (jerking) or stalling, and you'll control the speed with the clutch. All this was taught in MSF, but it needs to be practiced until you are really comfortable tooling this heavy machine around in tight quarters.
If you haven't seen the video Ride Like a Pro , get a copy and watch it. When you see Jerry and his buddies toss those Goldwings and Valkyries around the course, You'll realize that on a Harley that weighs over 100 lbs less, you can surely do it to with some practice.