An important point to consider:
Don't give in to the temptation to use a junk cube because you don't want to mess up a good cube while learning.
This may be fine for really basic practice (cutting, jigs, etc.) but before you know it you'll have spent a huge amount of time on something that is looking good only to realize it will never move better than the junk you started with.
I made this mistake with my Kilominx prototype (here
), and spent way too long trying to make it move well when the real solution was to have started on a decent puzzle to begin with.