Save the Trumps for Last
I hope it's okay if I contribute, though I haven't done a deck yet; I have a suggestion based on observation. I recommend, at least to less experienced or first-time deck creators (like me):
Save the Major Arcana for last.
I don't mean you should design the trumps last; I mean you should complete them last.
The reason is, I've noticed on some decks that the art on the Minor Arcana is really great; but when I get to the trumps, they seem...a little less great. Not bad, exactly, just...somewhat...um, lackluster? compared to the other cards.
After much pondering, I made a guess that it's because the process of doing an entire deck makes you grow as an artist. The trumps, being the big, important archetypal cards we're all really excited about when we conceive of a deck, get done in the first burst of enthusiasm; then the courts and/or aces, and then, finally, the number cards. By the time we've finished all those pip-card scenes, we're much better artists than when we began. But our Major Arcana remain as they were, the product of our less-experienced skills.
The Trumps should be the culmination of a deck, the cards that truly represent the ideas behind it. How much better would they turn out if we saved them until we'd practiced our skills on those forty, sixteen, and four others cards? We may even have gotten a few new ideas as we worked on the deck as a whole; doing the trumps last would guarantee that they would truly reflect the essence of the deck as a whole.
The way I'm planning my deck is I'm designing it as it's coming to me, doing Majors First for the most part—but only for the concept sketches. When I actually start the "final" stage, I'm going to do the numbers first, then the Courts, the Aces, and the Trumps last of all. If I just can't stand it, and have to get some of the Majors out of my system, I'll make sure I leave them in a somewhat "unpolished" state, so that (hopefully) I won't hesitate to start one over if I feel I could do a better job later.
Well, that's the sum of my idea. As I said, it's based on observation rather than experience...but I hope it might prove useful to others nonetheless.
ShinyAeon