How can you write a Genre story without copying other stories in the Genre?

Genres are like Adventure, Romance, Fantasy ect...
Also i find that it helps to either draw or write a description about your main character/s and then just let your imagination run wild... i'm writing a book as well but mines a collection of short stories.
Also if theidea is already in use use that idea as a base and eventually mould it and personailze it until it is different which i have done as well...