Decide what the theme and tone of your soap opera will be. Will it be campy or will it be melodramatic? Will the stories be family-based or will they be professional-oriented (like "Grey’s Anatomy," for instance). Determining what the theme and tone of your soap will be ahead of time will help you along the way as you write the characters and stories for your drama.
Create a setting for your soap. Setting is always important in writing any story. Where will the soap take place? In a small town? In the big city? Or perhaps in a bedroom community, a la "Knots Landing"? Will it revolve around a hospital, a police department, a university? Once you’ve decided where your soap will take place, you’ll have a better idea of the kinds of stories and characters you’ll want to create for your soap.
Every soap has a core family or families. "As the World Turns" has the Hughes family; "All My Children" the Martins. A core family creates a hub from which you can build a network of characters and relationships. A core family doesn’t necessarily have to be biologically related. For instance, "Melrose Place" created a core set of characters through the apartment complex where they lived. The significance of a core family or group of characters allows you as the writer to build an organic network of characters who will interact with one another in believable ways. You should have a better idea of what type of core families or group of characters you want to create for your soap after choosing the theme or tone.
Create your characters. Who will populate your fictional soap world? Start with your core family---build the different characters in the family and their core relationships with one another. For instance, will your core family have a matriarch and patriarch? Or will either be divorced or widowed? How many children will he or she have? Will they be children or grown adults? And will they be married with children of their own? Once you’ve created each character, determine how many supporting characters you’ll need. Usually, the supporting characters will have established relationships with the core family. These can be established through marriages, friendships or working relationships. As you build on these relationships, you’ll have a network of characters who will naturally interact with one another. Most soaps tend to have archetypes, for instance the good girl or the villain. Archetypes allow you to create the tensions each character will bring as they each pursue his or her own goal, often in opposition with one another. But remember, an archetype doesn’t have to be flat. Always create characters who are believable and real for your audience.
Write a back story for each of your characters. A back story is a synopsis of your character’s history prior to the first episode of your soap. Through your back story, you can establish your characters personality traits, their history and relationships with other characters in your soap (childhood sweethearts, old rivals, traumatic or life-altering events), their professions, educational and social backgrounds. For instance, let’s say you create two core families whose patriarchs are rivals. Why are they rivals? Perhaps the matriarch of one family had had a long-ago affair with the patriarch of the other? Maybe one of the children from the families is a product of that illicit union? A back story like that could create years of future story lines for your soap.
Build a story outline. These are called "bibles" in the soap opera world. Bibles outline the stories you will write for your characters. Sometimes, a bible can run from 6 months to a year. A bible should never be confused with the actual story, but merely a synopsis. Therefore, the bible should have a broad overreach of the stories you will be creating. You don’t have to be detailed in the synopsis. Rather, create a general outline of the story’s plot.
Create breakdowns from your outline. Breakdowns are daily or weekly story outlines which map out your stories in more detail. In other words, they are outlines for each episode you’ll write and the scenes within those episodes. Here, you can be as detailed as you want, including the number of characters who will appear in each episode and the emotional tensions that each character will or should be experiencing in the scenes. Depending on how frequent your episodes will appear, map out your breakdowns at least 3 or 4 weeks ahead of time. This will give you more leg room to know where your story is going and to make any adjustments or corrections along the way.
Begin writing your stories. Take your time in establishing exposition (after all, it is a soap), the various relationships and back stories of your characters. But also get started off with a bang. A wedding or a funeral is a great way to get your soap off the ground and establish the relationships between your characters.
Most networks are not accepting or creating new soaps at this time. Your best bet at getting your work seen is publishing it on a website. Or, if you have the means to do so, create your own episodes for streaming video channels such as YouTube. Acquaint yourself with your local acting, theater and filmmaking community and try to set up connections. Perhaps you’ll find people who’ll be interested in getting involved in your soap venture. Even if it’s not for profit, it will provide plenty of experience in soap writing and production.