How do I write a good soft magic system? I want my story to have magic, but I want the focus to be on the politics, the drama, the romance with the magic being a tool that helps move things along rather than the driving force of the plot.
If all the ranting about magic rules I've done lately has not convinced you I'm pretty bad at magic rules, I'll go ahead and say I'm probably not the greatest person to ask. Still, let me try to be helpful someone.
Soft magic does need rules (but only you have to know them) - as a background hum of your world, you do need to have a pretty clear idea of what magic does and doesn't do. But as a natural part of your plot and not the core of it (aka this is not a magic school setting where we are learning about the steps of magic along with the students), think about the rules of magic somewhat like the rules of driving. The characters know how to drive, and you do too. In a contemporary novel, you're not going to explain why someone stops at a red light. But you will point out when someone violates a driving rule - blows right through that light, or gets into a car accident. As such, when magic plays a similar role (a spell backfires, an attempt to do too much causes an accident), you'll be able to establish how magic works and doesn't work.
For a more concrete example, you don't have to explain how a cleaning spell works if it's something everyone uses. You do need to explain your rules of magic if someone uses the spell wrong and it blows up in their face (too much power, the wrong ingredient, etc).
Soft magic also needs limits (which you need to reinforce) - Let's talk about some really obvious limits - vampires can't go out in sunlight (unless they sparkle), werewolves can be killed with silver bullets, Spider-Man can't fly. You can establish limits with throwaway lines ("I can make plants grow, but I can't create them out of nothing"), little actions (someone uses magic to lift a book, but struggles to lift heavier things), and of course, plot-relevant events.
As long as Dracula doesn't go waltzing out in sunshine without an established reason, you should be good. You can introduce his limits via action-related plot (he can't chase characters once they flee the underworld into daylight), but you don't need to repeat it every chapter.
The reader won't have questions unless you introduce questions - In the novel, it's not possible for the characters to blow up the sun. Your magic rules don't work that way, so it's not something anyone would ever think about. Therefore you don't have to introduce the idea that magic can blow up the sun just to establish it can't happen
I think establishing magical rules and their limits tend to be overblown sometimes. I'm not reading a novel to catch a writer out on some weird magic mistake, and it doesn't stand out unless it completely contradicts a previously established rule. My last rule of thumb is to read Science Fiction. Many sci-fi novels drop you right into an unfamiliar world and have you learn how things work as they happen. Neon Yang's silkpunk fantasy novellas are a great example of this.