What do you even want to hear? You just sit down and write. The same way you did with the shorts. Write a sentence at a time, a paragraph, a page or even a chapter in a sitting. For some it takes a day, for others a year, a decade, a lifetime but one day you'll have a novel at your hands. All the fancy stuff, like overhauling the characters, the outline of the summary, etc, etc is done on the side when and if you need those. Some write with a plan, others by intuition. This is art, there are no set rules for this. If you get ideas for something far ahead, you just take a note and place them far ahead in your manuscript. Ideally, you set a goal of 100, 200, 500, 1000, 5000... words a day and keep track of this. You can do it without a schedule too. It's not like you are getting paid, nor is it like you can properly control your creativity. As for editing and beta-reads, some do that simultaneously, others after the entire work is finished. Anyway, just sit down and freaking write!
