"I've also signed up for a photography class dealing with exposure. I'm curious if anyone has some advice for me on how to take these photos from good to great."
How to take these specific photos from "good" to "great" is now a matter of software.
The photos have been taken and there is little you can do to change the actual image from the camera without resorting to software. Depending on how you see the process of photography as it relates to digital imaging ( and photographic imagining), you are faced now with either the greatest benefit or the most significant detriment to your process as a photographer.
The "greatest benefit" school of thought is that your digital image is never a completed product. Using more powerful software can continue to alter and shape the image in ways which had previously been difficult, if not impossible, to manage with analog film. It is now only a matter of what you choose to do to refine the existing image that matters.
Head to you tube and browse the videos for a very common piece of software such as PhotoShop or Lightroom. It shouldn't take long before you get the idea the image in its most basic form - as taken from your camera and presented as a RAW data file on your computer monitor - is merely a recipe card for how to bake a cake. The RAW file and the image it presents will tell you whether you are going to create an angel food cake or a devil's food cake or a bundt cake. Taking your shots in particular, you would want to mix portraits with landscapes and work with both to create a whole product.
Notice how the software can reshape the individual bits of your image and turn "blah" into "bingo!". Software will allow you to correct many of the issues with exposure on both a global and a discrete level. Colors can be remixed with software and subjects can be made to show more luminance and more vibrance. So on and so on. That is what you can do with an existing file. This is all you can do with your existing files.
The "detrimental" side to this is found in several issues. First, the most powerful software is often the more expensive software. That means your investment in photographic gear does not stop with a camera and a lens. Nor does your learning process cease once you have aperture and shutter priority under your belt.
The more powerful the software, the more there is to learn and to master. The more powerful the software, the longer it will take for most people to gain an upper hand over the software. As with your camera, you will be on a continual learning curve. Your image is never completely baked and frosted, ready to serve, but rather ready for another go in the oven in six month's or six year's time. Just as with your camera, what you do today will not be as complete or as "professional" as what you may do tomorrow.
That, though, is all you can do with these particular photos. They are finished as far as what you can do without software.
Making your photos "more professional" begins with patience. No one starts off by taking professional grade photos. No one.
Owning more expensive gear does not automatically make your shots more professional. Learning how best to control the equipment you have is your first step toward turning out better images today than you did yesterday. As with the learning process of imaging software, what you turn out today is unlikely to be as good as what you may turn out in six month's or one year's time.
"Professional"? AAA ball is much better than college ball but it is in no way the same quality as professional ball. Strive for what you can attain and don't worry about the rest. Professionals do this for a living and their investments are paid for by their production. Unless you intend to do this as a life's work, do what most other hobbyists do. Which is, accepting you do not have the money invested in gear and time and assistants, etc. to turn out "professional" quality photographs. And that advancing your skills will require time and experience.
Take these shots and hold onto them. You cannot now do anything with these images that doesn't require software.
Be patient and learn. Learn mostly by doing. Strive to make every shot better than the last. Never take just one shot and assume it is the shot and there are no other or no better shots which can be taken.
If you wish to improve your photography, there are multiple paths to achieve that goal. They have been widely covered in the archives of the forum. Read those archives. They will be more helpful than a critique of one or two shots.
As you can see, many people will present many ideas for how they would have taken your one shot. Learn from others but develop your own skills and, possibly, even, your own style of photography.
Unless you are going to digitally manipulate these images with software, set these shots aside. Come back to them in six months and after one year's time and notice what you feel you could have or would have done differently after you have gained some experience with your camera, your models/subjects posing/positioning, your photographic imagination and your eye for an image.
If you come back to these shots at those times and feel you could not have done any better, fine. You would, though, be the very rarest of photographers if you do not see many of the flaws and coulda'been alternatives in these images for yourself.
You learn photography by experiencing photography. Both your own and that of others. Take your time to learn and you will eventually see where you need to head. But, for now, these shots are done.