Are you going to be working in 104? If so, maybe choosing some of the stiffer colors would be best - until you get a feel. Of course, the probable combo of black and white hold their own integral complexities - white has to be one of the most "soupy" colors ever; and of course, coupled with black, it just wants to bleed! If you're using black, try Hades...it's the bestest BLACK GLASS EVER!
I have a couple suggestions:
1. Map out, on a scrap of paper, the layout of how you want to "stack/layer" your glass. Below is an example of how I did my Skull murrini. I'd had terrible trouble with it until I did the "simplification" of this mapping. Using "circles" drawn on the outline of your image (representing the stacking/striping of rods), this will help you decide, layer by layer, how to "stack" your colors:
As you can see here, I started with a gather of white, which I shaped into the half-round upper portion of the Skull. Flipping it over and working layer by layer, I built the remainder of the image - and you should use clear to "fill in" where there is no image to help hold your variably-sized shapes (such as where the upper jaw tapers on my Skull).
2. Consider getting some sturdy punties - I had difficulty with boro punties, so I bought some of Noodlesaurus' steel punties. They are amazing and stable for larger gathers. Here's a link in case you're interested:
http://www.noodlesaurus.com/catalog....Fcategory%3D17
Here's my resulting murrini, along with the "test" micro marble I made, quick-quick, just to see how it looked:
3. If you have a steel spatula, this will help to "square up" your flat edges of the squares in the checkerboard, color by color.
Good luck with it! Hope this helps encourage you to give it a try! It may take a couple runs, but I'm sure you'll get it!
De