Normally, I'd say start a romance with a gorgeous, rich, single man with a private jet and a villa in Monte Carlo. But for the next several weeks, we mean How We Start Writing a Romance.
I start with concepts drawn from my life. For example, I prefer homeopathic medicines over allopathic drugs. Concept: Parents of a 23-year old woman clash when she and her mother choose a naturopath to treat a lump in her breast. (True story. A year later, she was pronounced cancer free.)
This isn't very romantic, so I start playing with it. A medical doctor arrives in a small, rural, northern town for his first post-residency job. A local woman makes herbal remedies--tinctures, salves, teas--that many townspeople swear by. Doctor and herbalist meet and clash. Still, they are attracted to each other. As they are trying to get past their differences, an antagonist takes advantage of an external crisis and drives a wedge between the lovers.
I have now an idea for my setting, as well as some rudimentary information about my hero, heroine, and antagonist. My next step is to think up names. The bad guy's name should conjure an image of a nasty, selfish, greedy person. I'd have to write hard to make Fred Smith sound like a dashing doctor. My herbalist heroine can pick the name of a wildflower used for tea.
While my names are steeping, I think about the characters main qualities and their backstory. Did he work his way through college? Was she an only child? Who taught her about plants?
When I have developed somewhat her background, I pick her Sun sign. I know her place of birth--small, rural, northern city. I pick a birth date, and guess at a birth time. Then I test possible horoscopes. Interestingly, it never takes too many attempts to generate a usable chart from which I get a detailed personality profile. (Repeat for hero and antagonist.)
By now, hopefully, my names are brewed. I have backstory on my main characters. Now it's time to plot.