If you're planning to grow veg have a look at Huw Richard's book 'Veg in one bed'. It gives a month by one guide of what to plant and tend each month, starting in March. I'm following it for one of my beds and so far this year have had potatoes, broad beans, lettuce, radish and currently have leeks, kale, purple sprouting broccoli, chard, beetroot, runner beans and dwarf beans, and I've just planted turnips, kohl rabi and pak choi. I have carrots still to plant and some more salad leaves/mustard during August. My bed is bigger but not huge, so there's enough space for quite a variety if you go for succession planting.
My beds were made last year when I had the garden landscaped. The base is hard core and the landscapers put bags of compost in. However, I've since added topsoil as I found the compost wasn't substantial enough, and have continued to add a couple of bags of compost and some chicken manure pellets (for plants beyond seedling stage).