how to "improve" the soil will largely depend on what its like already , and what you want to grow
but in general terms you ought to double spit dig (that is dig to twice spade depth , turning the contents of each trench into the one dug before) over the area you want to use for veg, flowers etc - whilst doing this pick out all the bits of rubble, of which as you have already found there may be quite a few (if you pile the rubble up in a quiet corner you can create a nice wildlife habitat at the same time)
having double dug the area once , you need to go back over it again this time adding stuff to improve the soil - what you add depends on what the soli is like, if you want to improve drainage you add sand , to improve nutrient content add manure or compost (not peat based for eco preference), to neutralise a acidic soil you add lime so forth , so fifth.
for the negatables you may also want to construct some raised beds - basically raised areas which are well dug , then not walked on in future meaning that future digging can be kept to a minimum.
you might find these links useful
Points About Root Vegetables You Already Know or Should, Some Thoughts for Beginners http://www.recipes4us.co.uk/Growing&...Vegetables.htm BBC - Gardening - How to be a gardener - The productive garden - Growing vegetables Growing vegetables in raised beds
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