You may have only a vague idea of where you are going.

You may have only a vague idea of where you are going. That is all right. The objective here is quantity, not quality. Still, your story will be easiest to write if it is interesting. Do not be afraid to throw in a complication. Kill a character, have somebody get pregnant, bring in a new villain, or reveal the extent of a character's flaws. Then, see how your characters react. Take the plot somewhere, even if it is not where you intended. Sometimes the surprises are the most fun