Posted: 08/08/2013 at 14:32
Hi Mark- you have a bit of a task there! As you say clearing all the debris and starting with a clean slate is the best thing to do. It may take a while but in the meantime you can start planning what you want from the space. If you can give us an idea of the aspect- including any other buildings etc nearby that will cast shade- that will help with plant suggestions, and also tell us what the soil is like and what the overall size is. If the plot's very shady for instance, it's probably not worth having grass. If you want to get some trees back in, go for some of the airy types like Birch which won't give dense shade, or the ornamental cherries or almonds, depending on how much room you have and what else you want to plant. Amelanchier is another useful shrub which can be grown as a small tree. Make a list of the things you want to have- ie patio/dining area, veg plot etc and make a little sketch of where those things can go so that you can see what you're left with for general planting. If there's features outwith the garden that you want to screen, include those too.
Hope that's a little help to start you off. In a way it's good that you're starting now, because you've got a couple of months of decent weather to get the clearing done and that means you can take your time planning over the winter to get going in spring!