1) Paint fence and the wall white - this cleans up messiness and brightens the whole space. It also unifies the disparate vertical surfaces. 2) Weed and Prune, but not too much — leave a few things to climb the walls. Also be careful not to raise the canopy of the tree too much — having a low 'ceiling' in a garden is a really nice feeling.
3) Install Cobblestone patio — Cobblestones are a great material for a small DIY project. They are easy to move, easy to work with and the end result has a lot of character.
4) Finish with rustic wicker furniture, a pretty light in the tree and other decorative elements like baskets and squishy pillows. If you read Swedish (or use google translate) — you can read a bit more about Katarina's project on her blog, En Gron Sida. (Images: en gron sida)