I haven't made a deck that has been published yet, but I think maybe my experience with the first run can help. When starting over, my first step was to create a template for the deck to make sure I have a consistent card size and print-quality resolution (300dpi is a good standard).
Making some decisions about the overall gameplan might help as well - do you plan a full deck with majors and minors? How detailed will the minors be? If they're full color, full quality, it's going to take much more time to get through them all, but it will likely impact the amount of people interested in your deck.
I think another important decision is whether you are going for a collectible art deck or a more traditional deck for people to use in readings. If you go too crazy with the interpretations, it may look gorgeous, but people may have a hard time recognizing the cards in the reading.
I've read a few stories about people having a hard time getting their decks published because their theme was one that somebody else had done. I'm not suggesting you limit yourself creatively, but if you go with "Grimm Fairy Tale Tarot" as your theme and there's already a Grimm deck out, it's going to potentially hurt your chances to see it published.
I by no means an expert, so people may contradict me here, but I did make a complete deck about 10 years ago so I do know how tough they are to finishe and to publish