Thats a lovely wall that you have in your garden.
I have found that you can get some very cheap books on garden design online, amazon and ebay are a good place to look.
I am also inspired by many photo's here on this site.

What sort of ideas are you looking for?
Do you have any idea of what style of garden you would like, does it need to child friendly, would you require it to be low maintenance, what is the aspect of the garden, do you have a budget?

You can always pay a landscaper or look through some of the hundereds of photo's on the site for ideas, that is what I did.

Don't forget your public library - no need to go buying books when you can borrow them for free!

I think you need to decide what you want from your garden and how you wish to use it? So why not make a list, do you have pets, children to consider? Do you want formal, informal planting, do you want to grow veg, do you want to sit in it, encourage and feed wildlife, are there any styles you already like? What dont you like? Also how much maintenance do you want to do per week/month? Finally what conditions do you have light/shade, wet/dry, clay/chalky soil, windy, slopes? and at other gardens and see what grows well in your area.
Above all do your homework research need not cost anything! but by deciding what it is you want will give you the confidence to make a start. My tip is not to try and do it all at once, divide it up and do a small area first and enjoy it.