Where to start? I've noticed several members of our Color Art for Everyone Facebook Group are unsure what/why/how to use a particular medium, what shades of colors should be used and what type of coloring books are preferable.

I can offer suggestions and some practical advice, but being artistic lets you experiment. Everyone can show artistry. Some people's results may be more refined than others, but it is all part of artistic self-expression. It's up to you to be adventurous and have fun! Let loose and try it out; that's the benefit of stress-free coloring.
Along with your choice of medium, you may want to (re)familiarize yourself with colors. A good example of how colors can work for you is found by viewing a color wheel. Here is a basic example of how to use a color wheel.
Don't restrict yourself by using only one medium in your drawing. Coloring is about experimenting, as well as, disconnecting from the logical part of life. Here are some good examples of combining different media.

Should you consider what you desire as your end result? Sure; the look may change your mind in what medium to use. Also, are you planning on giving your page as a gift? Does your answer affect your choice of medium? It may; so here's a page showing result comparisons that may assist you in your decision.

You don't need the most or best in your media choices. You can have rich, colored pages emerge if you practice. As a post-baccalaureate student a few years ago, my Photoshop professor reminded the class of layers and applying layers of color as we see in a painting. It was a great example to think of fine arts as applied to digital art for desired results.
Start with single colors applied multiple times in each design area. Use this idea to create your colored pages. In the example below, I have made my choices of color and have started to apply the first layer. In some areas, you can see more intense colors emerge as I have applied additional layers.
In my project below, the page's repeating design reminded me of wallpaper. Continuing with this idea of applying layers of color, I moved on to the next step by introducing several colors to each design area. I wanted to decide on colors that repeated as did the design, but I also wanted to show dimension within each character of the design.
In the next two examples, I have used markers to create a dimensional effect applying several shades of color in each flower; and, experimented with gel pens and watercolor pencils used with (regular) colored pencils in the page showing the many strands of shells.


Now, I wanted to experiment with new applications creating different blended effects. Using petroleum jelly to assist in blending is new to me but has received a lot of attention recently. First, I decided on a page of waves; a page that could express movement from the book Art of Coloring Coastal.
I started with a simple, light layer of colored pencils in my waves. I then began applying petroleum jelly. There are different methods to apply the petroleum jelly, so do some research and try them out. After my first layer of colored pencils, I dipped a colored pencil of choice in the petroleum jelly and started coloring. The petroleum jelly is used from the pencil tip very quickly, so reapply often. I then decided to return to the area with petroleum jelly and blend by rubbing with a cotton swab. You can see the progression of my page in the following images.




In the two images below I show a close-up, then a summary of steps used to create different looks. First, I show waves using colored pencils as my 'base' layer, with the next layer being watercolor pencils applied on top. Next for your review, I outlined some of the steps by placing notes on my page.

Another reason why I love our coloring books is their paper. Look how well this page has held up with all of my experimentation using multiple layers of colored pencils, petroleum jelly, and watercolor pencils.
Some tips I have learned: Don't dip too deeply into the petroleum jelly because you'll only get a clump on your entire pencil point -- and it will get too messy on your paper. Re-dipping and applying often is best. Wipe your pencil clean, gently blot the paper with a clean paper towel, and leave your page open to set.
This post holds a lot of information - and it's incomplete; there's always more! Use your judgment after you try things out. I offer these ideas as suggestions - learn by doing and sharing your experiences with us; join our Color Art for Everyone Facebook Group for the easiest way to share. If you're looking for new coloring books, visit Leisure Arts today.
Another thought on the construction of coloring books. Before the resurgence in their popularity, whenever I found a grown-up coloring book, I thought those with spines were better -- until I tried to open up to the page I wanted to color. The spine needed to be broken in order to lay flat; not great for a book's life. For me, saddle-stitched (stapled) books with perforated pages are key! The perforated pages give me the option to remove my pages when done. Oh, yes; I keep my pages intact in their respective coloring book while I'm coloring. I have no difficulty in coloring the entire page because they open to lay flat on any hard surface. My pages in their books travel safely with me -- great transportable entertainment!
Have fun --
Martha