Try and get hold of the RHS book - The Vegetable Garden Displayed - ISBN - 0900629 13 4, it explains all about crop rotation and sowing times, and about digging and green manures, etc. About now in the UK, you need to be sprouting your early spuds ( they are best grown in containers) planting shallots and garlic while it is still cold, to cause the cloves to form, peas and broad beans can be sown now, unless you have loads of space and plenty of canes grow dwarf varieties. Start digging some trenches and filling them with manure and compostable food waste for runner or french beans to be sown early June(French beans are probably best because they tend to be smaller, you will need about 8foot canes for runner bean supports) Dig a few pits3'x3'x3' and fill with manure and compostable food waste so that each one is capped of with garden soil in a slight mound, these are for growing marrows, corgettes, and squash, pumpkin, etc. sow in 3"pots on the window sill, 2 seeds per pot, when the first true leaves show, discard the weakest plant in each pot, then plant out the stronger seedlings in their stations, which should be about three foot apart, water in well, and keep well watered. I planted 4 courgette plants last year, and got zillions, they lastyed us and the neighbour hood until October, when I pulled the up cos I needed room for my onion, garlic, and shallot sets.