How I plan to get a story idea, (this isn't all the ways but this one is fun so)

Step 1

Princess
Desert Island
Banished by father

Here I have begun who, where and why.

Step 2
Fleshing out step 1

Princess Faye living on a desert island of sandstorm. Banished there by her father after falling in love with the son of his mortal enemy.

Step 3

Demons
1,000 heads
banished mysterious knight

Step 4

Flesh out st3

To end her banishment she must cut off a thousand demon heads and give them to the ghost of mysterious knight.

And I just keep going until I have solid plot, the beginning, middle and ending so I clue what story I want to tell.