That's very vague, but I guess you have to try and find what exactly your characters relationships are. Then you need to get your setting, you have many settings to choose from, Steampunk, past, fantasy, sci-fi, cyberpunk, modern, post-modern etc. You need to ask yourself which settings do and don't work for your story, I'd start with the settings that wouldn't work (or you're not interested in) like if your characters have an online relationship, a story set in the medieval times probably wouldn't work out so well. Then once you have your setting you need to see if there could be some initial conditions based on what you already want your characters to be and based on what the setting is. Lets say you have a shopkeeper who hangs out with a friend, but you picked the medieval setting, well then that shopkeeper could be a blacksmith. Then you can add onto their individual stories and say maybe he is a blacksmith for a family of 2, trying to make ends meet. I think that it's important to have one centralized theme though, something that all the side stories somehow relate to, lets say the theme was a treacherous king, then the blacksmith could be finding it hard to pay for his family due to all the kings taxes. A centralized theme I believe is very important, the characters relationships should add the depth to the story, but you need the basic skeleton that those side stories relate to. Once you have the setting, the initial conditions and the centralized theme, you need to have a complication in the centralized theme (and the relationships). A story isn't interesting if something bad or unexpected doesn't happen at one point, so you need to think of what your complications could be, in the case of the medieval story, maybe the a rebel group for the king has arisen and the blacksmith is with the rebel group but his lover is with a follower of the king. Once you have all that, you finally need to make a conclusion or resolution, something has to happen, people usually prefer good endings, but with a bit of a bad touch to it. For example, the treacherous king is overthrown by the good rebels and the land is saved, but the blacksmith's wife leaves the blacksmith and is banished out of the land. It's both good and bad.
I hope that helps.