What you need:
1) felt in any colour you like...even not natural leaf colours will look pretty.
2) thread darker than your felt.
4) actual leaf or leaf template
Firslty draw round your leaf/template onto the felt and cut it out. Fold felt for cutting more than one at a time...(speed trick)
Secondly with the darker thread sew the leaf vains either with machine or by hand.
You can copy real leaf vain or estimate where you think it should be.
Thirdly either sew them together for a hanging or to go on collars or cuffs of jumpers. Or attach to bags,headbands, pencil cases,as belt, frame.hair clip,necklace etc....
options are endless.
P.S felt doesn't fray but can shrink in wash so, dry clean items such as jumpers with felt on.