You can take a pattern that is normally a shuttle and ball thread pattern and turn it into a two shuttle pattern (in lieu of ball thread you use another shuttle).
Why would you want to do this?
Well it opens up some options like "floating" rings.
Take the above motif for example: Half of the motif is tatted in the regular way (shuttle = rings, ball thread = chains, tat a chain, do NOT reverse work, tat a ring, do NOT reverse work, tat another chain and you get a nice pointy effect).
The other half is tatted by the "thown off" or "floated" ring method.
Shuttle #1 = Yellow thread (Ring)
Shuttle #2= Red thread (Chain)
To "throw off" or "float" a ring you simply use your chain shuttle (#2 in this case) to make your ring instead of using your ring shuttle (#1).
Once you understand and utilize this 2 shuttle tatting method you can "tweak" patterns to suit your personal taste. Pointy verses Round, also if you tat with two different colors you can have control over the placement of your color in pattern.
Another thing to think about is which direction the top your chains are facing. This does make a difference in the shape of your end product. How do you do this? Please visit my Turn Work VS. Reverse Work tutorial.
For future reference all my tutorials can be located in my side bar to the right.