It is cool you are interested. My advice as someone that spends a bunch of time thinking about and developing card games:
Design: Start with a core activity that the player can do, and have them naturally move toward that goal over time. Also, since your starting out: keep your scope small. You can make it bigger later.
Engine: I had some trouble with my engine at first, so I would start thinking about ways your engine handles lists, arrays, or sets of objects. If worse comes to worse, you could roll your own data structure. Also, each card is obviously going to want to change between them, so, cards will need a few variables.
Inspiration: On your smartphone, if you don't already have a program or a file like this, download a word processor, and make a new document called "Ideas 20XX." Whenever you have an idea, write it down in this file. You are going to make a new file at least every year, because large text files can get sluggish, even if you use Microsoft Word on a modern desktop (ask a dude with a 200 page GDD).