As others have already said...
1. Create Character A:
- Who is this character? What's his personality? What are his hobbies?
- What was he doing this morning? Last night? The week before? (just examples, you don't actually have to answer these, but it can help)
- How tall is he? How much does he weigh? Other physical appearances?
- What does this character want to do?
- Describe this character in one sentence.
2. Do the same for Character B.
3. Create the all-too-important setting:
- Where is this story taking place?
- What makes this place special? Its history? Its sights?
- Describe this place in one sentence.
4. What happens when Character A meets Character B?
- How did they meet?
- Where did they meet?
- Who initiated the conversation? How?
- What happened during the conversation? What did they do? What did they talk about?
- What resulted from the conversation? What is this scene leading to?
5. Is there a problem? How do Characters A & B solve it?
Now rinse and repeat the last step. Make more characters if you wish. Change the setting.
The way I do things sometimes is I just put a character or a few characters together in a random setting... like in the corner of a coffee shop, and just have them talk. They'll just talk and talk and talk and by constantly writing their lines, I can imagine them in different scenarios (and it really helps to try to really imagine and get into these characters' personalities, kind of like acting), which in turn allows me to outline different situations where I can place these characters.
I'll do one for practice right now.
Setting:
Northport High School for Arts & Sciences; the surrounding town and neighborhoods
(I'm not going to describe the setting here. Let's just keep it as a generic, semi-quiet town with a medium sized population and household income. Everyone's pretty much chill.)
Character A:
His name is Mikey. He was an all-county shortstop his previous year (sophomore). Due to family circumstances, he had to switch schools and he's feeling pretty crappy about that. He's even lost interest in his favorite activity (baseball). Solidly built, but not a total musclehead, he's got the looks and the personality to be successful. However, this situation is just rough on him so he doesn't really present himself the most positive light. After all, he doesn't want to be here.
Character B:
Her name is Jane. She's the captain of the girls' softball team and Mikey's classmate. She's stoked because she's always wanted to befriend a new student at the start of a new semester. She also technically transferred schools, but she was fortunate enough to do so her freshman year. Mikey doesn't seem particularly interested in anything and just goes about his daily student routine and Jane finds this odd. She's rather intuitive so she asks if Mikey would like to come watch the next softball game. This strikes a nerve and Mikey is reminded of all the things that didn't go his way recently.
And now I can write a massive script between these two characters and perhaps mutual friends between the two. They can argue, they can be stubborn, they can act out of goodwill, they can get hurt, they can cry, they can laugh, etc.
And now my brain's flying through scenarios as I'm typing this. Now the story can be Mikey accepting that he has a new life now and can't dwell on the past. Jane convinces him that the future is bright. Mikey tries out for the school's baseball team and nails down the shortstop position. Jane continues to support him. Mikey gradually starts to really like the new town he lives in. In a league match, he loses to his old team (oh, no!). He feels down for a while, but he's reminded that he has Jane and his new friends supporting him. He works hard to not betray their kindness. For the climax, at some point Mikey faces off against his old school's team again and wins. Happy ending.
Ta-da. Insert mucho descriptions and details in between. Add more scenarios since we're talking slice of life. After school activities. Going out on a stroll in the park. Running your bike into someone, bam, new character intro. Getting locked in the bathroom. Getting called to the principal's office for unknown reasons, starting an arc of silly mystery and face-palming gags. Mikey meeting an old classmate from his previous school that took his old shortstop position, oh snap! Another student from his old school transferring to Northport, what's going to happen? I dunno, just making stuff up here.
All sorts of unanswered questions based on the random descriptions I made for the characters can also be fleshed out extensively:
- What were the family circumstances that led to Mikey's transfer?
- How was Mikey's life back at his old school? Was he truly happy?
- What did he do when he first transferred that negatively affected his image?
- How great is Jane as a softball player? How did she become the captain (or is this even important)?
- What's Jane's story when she first transferred during her freshman year?