I would keep doing what you are doing, which is creating your own original completed pieces, but what I would also suggest is that you do value studies on the side. Some value studies that could be helpful would be to take art that you admire, turn them to grayscale, if they aren't already, and see how they are structuring their values, and how they are structuring their values around the focal points vs other elements like the background. Copying them will also help, but always think about the values you are copying, and why you think the artist chose them. If you are signed up for a subscription here, I highly recommend the Creative Composition course as it deals quite a bit with value and contrast.
Here's some examples of what to look for when analyzing artwork. All of these are by Will Terry that I've turned to grayscale.
In the image below, I have used the color picker in photoshop to sample the values in different zones. Look at how the sky doesn't have much range in value, making it a nice backdrop for some of the other elements. and while it looks on the light side, it doesn't have the lightest value in the painting. Moving on to the cliff, it has a pretty good value range, but look at it in comparison to the spider (including it's clothes). The spider goes from almost black all the way to white, where as the cliff behind it stays more in the mid-range and doesn't have as much contrast. If he had chosen to go darker on the cliff, then the body of the spider wouldn't have stood out. If he had gone really light, then the chef's hat wouldn't stand out. Now look at the two groupings of cactus/foliage. It has a pretty good value range, but again, look at them in comparison to the spider and the gordita. So what we can learn from this piece is that one way to make the focal points stand out is to have more contrast with greater value range, and put them on a backdrop that will allow them to stand out. On the less important elements, limit the value range.
Here is another example that uses similar principles.
Something I'm noticing in your work, is that in a lot of your pieces all of the objects look like their local value is the same value. For example in the piece below, the value range for all of the different elements are pretty much the same.
Look at this piece by Will Terry below. It's a good example of using different values on different objects. You get the sense that Harry's hair is darker than Hermione's and that Harry's vest would be a different color and value than that of his robe. Look at the value range of each element.
I think this piece of yours is probably one of the most successful in terms of value. Look at how you've kept the crab and water less contrasted in the value range, where you have contrasted more in the seagull, and given the different elements on the seagull different overall values. Well done!
I think learning how to structure your values more effectively would take your art to a whole new level.
Keep posting and good luck!