dig plenty of sharp sand into it and old grow bag soil

Presumably, where you live, you get some pretty sharp winter frosts? If you do, then dig the whole bed over, removing any weeds as you go, and adding any humus rich material you can get hold of, and horticultural sharp grit (large bags) at the same time - no need to work it in, just chuck it on and turn the soil over, leaving it in clods. Leave it over winter for the frost to do its work - it will break down those clods ready for you to plant in Spring.
If you don't usually get lots of frosts, or you want to plant this year, then dig over as described, breaking up large clods as you go, still adding the humus rich material and sharp grit. By humus rich material, I mean well composted horse manure, chicken manure, leaf mould, spent mushroom compost, home made garden compost, soil conditioning compost from the garden centre, anything like that, and as much as you can afford, depending on the size of the area, of course.
Sand is of limited use, sharp grit does a much better job on clay soil. Do not use unwashed builder's sand.

Before you can add anything to it, my friend who has a big public garden uses a pick axe to break up the clay soil!

Good point, lulu - though there are usually 3 or 4 days a year where its possible to dig it with a fork, lol!