I'm learning Z80 for programming the rc2014 kit (it's really nice kit if your also into electronics). There is a surprising lack of information online about the techniques of programming. For me that's the biggest struggle. You can know the instructions but juggling registers in an optimal way is hard. I'm currently learning I can use the stack inside a routine to have more values in the air at the same time, but then I read some example code and learn a particular instruction can be used in a clever way to avoid all my stack juggling. I am finding it can take hours to write a simple routine. I really get it now when people write it's a non-trivial problem to map C to assembly (especially Z80). Hell, it's fun though! Screw all these high level languages, let's do everything in assembly and damn the horses!!