Most Vegetables will need sun for some if not all the day. Find a spot in your garden where it will get between 4 and 8 hours sunshine in the summer (when we get the sun!) and don't forget that 6ft panel fences will cast a shade all day in some gardens.
Ideal soil for vegetables is described as a fine tilthe, which is well broken particles of soil so that moisture and nutrients can get in. don't worry if your soil isn't there yet, -either clay clods, or fine sand, when you use your leftover vegetables on your compost heap, you'll soon get a homemade soil conditioner perfect for augmenting any soil type.
An ideal sized vegetable bed can be reached from either side, so that they soil is not compacted between rows of crops. If you have a large area for vegetables (lucky you) then divide it into areas, - 1.2 metres wide is ideal.
I love raised beds, and have used them quite a lot in both my garden and clients gardens, - they can be used either to just define where the growing area is, or they can be made higher so that they are at an easier level to garden at if bending is difficult or if you need to protect from animals. There are lots of types on the market now, in plastic and wood, and they are almost cheaper than making your own.
When you've looked round your garden and found the ideal place, marked out where you're going to plant, then you're ready to start your plot. - Ready, Steady, Grow.