Place a small preformed Stillwater pond planted with water iris and a Lilly ...no fish... in the middle to create a focal point. Make a small path of red mulch going to the pond circling around it and then leading to the back. The rest of the area can be covered with black mulch to cover all the raw earth. Make little islands of annual flowering plants to give some instant color in areas of choice. Go to the GC every few weeks to find perennials in flower that you can plant so your garden will always have something in bloom during the growing season. You can also create secondary focal points with a few garden ornaments. In a previous question you were asking about obtaining some large garden rocks. These can be placed as focal points with plantings around them. You have a blank canvas right now and you can create a very nice small garden if you wish to.
Of course you know your lighting conditions so let that be one of the guides in obtaining your plants. For your perennials dig out an inground "pot" and fill that in with good garden soil when you plant...do not refill with the same soil you dug out. Part of these suggestions involve a quick fix and another part involves patience. Good Luck!

That's an ex lawn! You could reseed it if you want grass there. There's lots of advice online about preparing the ground for this, try the RHS site.

Ex lawn indeed, although you may get a little regrowth in what looks like the sandy area. If you still want a lawn there, either strip out the rest of it and returf, or try to scrape off most of the builder's sand, get a good tilth up on the top and re seed,but if you seed, you won't be able to use the area normally for 3 - 6 months. By 'normal use', I mean walking over it frequently, sitting on it, running on it, children or dogs using it...

Many thanks for some great ideas. I will have a good think about them, calling it an exlawn is really quite right?