I'm just a beginner too, but I'll throw in some things that I've found to be helpful. It's also a bit of a think on what I really need to work on.
As Chief already mentioned, along with getting the right moisture content, nothing will go well if the layout and swivel knife work isn't good.
My areas of focus are:
1) casing
2) accurate layout
3) accurate swivel knife work
4) "subtleties" of swivel knife work (changes in depth as lines taper out, correct angle, how lines merge)
5) coloring (tooling) inside the lines
6) even tooling where it's supposed to be even and shading from one depth to another when that's required
References:
Bob Park's Creating... Western Floral Designs was very helpful to me. I found it more about design than execution but it makes very clear what the different elements are about and how they should flow together. His article on edging has made a world of difference to me. At least producing nice edge doesn't seem to require a great deal of skill, just time. http://leatherworker.net/edging.htm
Chan Geer's Sheridan Style Patterns for Belts 3/4" to 2" has been a really good source of patterns for me. They range from those with somewhat larger, easier to carve elements to those that are smaller, tighter and more difficult. I still haven't tried to design my own patterns other than some cutting and pasting, and focus on trying to replicate what others can do. Start with big easy patterns so you can get the feeling of doing some things rightt! The reason I try to replicate is that I find it easier to compare my work to the examples and the many (too many) mistakes show up clearly.
Sheridan Style Carving by Gardner and Fay also helped. One thing they suggest is purposeful practice with the swivel knife on some set patterns. I like this as I can try cuts over and over until they improve without messing up a larger piece of work.
I'll try to add a pic with some observations.
Keep at it,
Dave