To plan the garden, you have to take into account how much sun a particular area has first of all. Plants that grow taller need to be on the north of shorter plants, to keep from shading them. Don't plant where the shade of a tree will cut the sun too much, but if you're planting cool weather crops, like lettuce, radishes, spinach... they can generally tolerate less sun and benefit from the cooler air of a shade tree. Check the seed package or plant for a general idea of how many hours of sun will be needed.
Watch your soil - which area dries out first? Which seems to stay boggy after a rain? Root crops need a loose soil and many thrive in even a slightly sandy soil, while crops that carry heavy fruits above ground need more stable footing. Even within a few square feet, the ground can have different tilth and drain differently.
My backyard is chopped up into several garden areas because I have a huge spruce centered on the south fenceline. It shades a good portion of the yard at any given time during the summer, which is great for sitting outside, but not so great for gardening. My raised beds are against the north fence, as far away from the spruce as possible. I have a privacy fence along the back side, so that cuts out the morning sun for 10 or 12 feet until mid morning, so I put the raised beds about that far from that side. I can plant things against the privacy fence that don't mind the heat because it gets full afternoon sun.
There's a small spot beside the back door that gets full morning sun, but only until the sun hits the zenith, which gives it 5 or 6 hours of good light. I grew okra there last year with some success, but it would have done better with more sun.
A lot of planning comes from experience. Sometimes you just don't realize how sunny, wet, cold, etc., an area is until you've planted different things in it. (At least I don't!)