Don't be tempted by big specimens, younger plants will adapt and grow faster. Then mulch with carpet or sawdust. Grafting apple branches on crabapple trees can have wonderful results. Try using a pencil sharpener on the branch, drill a hole of about 1-1.5 cm deep, fill with grafting glue and stick it in. Hippophae Salicifolia is this months 'guerrilla tree'. .
Green manures are plants grown to fertilise and create soil the lazy way.
Rake the soil surface, removing big rocks and other non organic material, spread seeds liberally, rake lightly again, water or wait for the rain. The ground will slowly start living again, and with a bit of luck plants will reseed and build up earth by themselves over time. Have a look at the list of which plants can be used, but the cheap and easy way to do it is to buy mustard seeds from your local corner shop. Comfrey can be found around, especially near canals. Dig out bits of roots and put them everywhere.