I think a good place to start would be observing where the light falls in your garden - figure out if it is north facing, south facing etc.
That will help you chose where best to build raised beds for your veg, which areas might best be suited to having a flowerbed dug in, and help you establish which plants would thrive best in which areas.
Observe where water collects, which parts might be a little soggier than others, or totally dry if they were at the top of a slope.
Taking these things into account will go a long way to ensuring you've designed things well and the plants you've chosen will thrive in the right spot for them.
For instance, the front of my house is North facing, so only gets a few hours of sun in the morning. When it rains, water really collects in this area. So I specifically sought out plants that could tolerate shade and moist conditions.
Do you have any mature trees or shrubs already, which cast shade?
If not you might want to consider adding some, especially if you're lucky enough to have a large space. These will add some much needed structure and vertical interest.
If you like quite an informal style, browse images of cottage gardens, these will give you lots of ideas for low maintenance, pretty perennials.
If you are putting in flower beds and borders, I'd dig in softly curved shapes, which will look much more natural and informal rather than straight lines and edges. Think islands of flowerbeds, perhaps in kidney bean shapes or ovals, or a gently wavy edged border.
Perhaps the veg growing area would be best suited close by the greenhouse/shed/lean to, so that area looks all together more productive, and the rest of the garden dedicated to 'pretty'?
Just some things to consider.