I'm glad you started this up! A couple of us were talking about doing something like this -- Treefox and I were having a conversation in comments on an art piece about "what colors are you using to achieve..." this or that, and I think that could be REALLY useful, since Copics give you the number/name system by which you can really identify what you're using. I think most of us come up with combinations to use in a hit-or-miss way, and it can be really hard to tell from the results what exactly was used. Or like, I'd love to know what others use, because maybe someone else has tried a color that I don't have yet, but that I'd like to try to get. Or, someone else's "formula" for caucasian skin-tone may be really different from what I use, but finding out could leave me to find a new technique I'd like!
I guess one of the main things to talk about first is: what kind of Copics did you get? (And, how many colors do you have to choose from.)
I think there are 3 main types of Copic marker sets:
Originals -- with one fine point, and one wide wedge point.
Sketch -- with one flexible brush-tip point, and one wide wedge point.
Ciao -- with one flexible brush-tip point, and one wide wedge point.
To be honest, I'm really not sure what the difference is between the Sketch and the Ciao lines. I think when I bought my first set, it appeared to me, on the website I was looking at, that the Sketch had a much wider range of colors available, while the Ciao line was more limited; but I'm not sure if that's completely true?
What I use, therefore, is the Sketch markers. I bought an initial set of 72, and have added a bunch of individual colors since, based on what I found I needed/wanted. (Some of which were kind of duds, because I order all of mine online, and sometimes the swatch doesn't quite match the actual color on the paper I use.)
The techniques that people use will vary a lot, depending on which kind of markers you have.
The second-most important factor in using art markers of any kind is what kind of paper you use. The same color will look different on different types of paper, and different papers will "blend" better than others. So experimenting on different papers is a good idea.
And a good tip: whether you like using a variety of papers, or just one -- take a sample sheet of each kind of paper you use, and then color a half-inch square of each of the colors you own on that paper; write the color-number below or beside it. I find it a lot easier, when I'm coloring, to figure out what colors I want to use, or what I should use next for shading, when looking at that guide, and the guide helps me reach for the right marker. Doing that also helped me figure out what the actual tone and intensity progressions were in the colors I owned (since you can't always go just by the numbers on the top).