Head out on a lovely autumnal day and collect as many natural items as you can. Variety is good, but even if you can only get a selection of different coloured autumnal leaves thats enough to work with.
You will need for your picture :
Nature items - leaves, twigs, bark, acorns, conkers, etc.
Anything else you want to use to put in the picture, suggestions are different coloured pipe cleaners, cotton wool, paint
Then get creating !!
Some ideas to help you along - You can use some bark to form a tree trunk, and then stick on various leaves, conkers etc... and use some autumnal paint colours, to add detail
You can make your picture a bit more structured, in the next example different coloured pipe cleaners and cotton wool have been used to add the sun and sheep detail.