Summarize this article:

For the best results in your garden, six hours of sunlight is suggested. So it is best to avoid putting the garden too close to your house or in areas where it will be covered by the shade of a tree. If you have lots of trees, houses nearby, or other things that would block the sun, you may need to pay attention to your yard for a week or so to find the spot that gets sunlight for the longest time each day. A tree’s root system can spread far out underground, even if you can’t see the roots. If you try to set your garden up too close to a tree, the root system will cause problems with your plants. Try to go at least 10 feet away from the furthest point out that the branches reach. As you start to dig later on, you’ll be able to tell if the soil has a lot of tree roots or not. If the spot you chose ends up having too many roots, it may be best to move to a different spot if possible. You need to find a balance between a spot that will not hold any water in the in soil, and a spot that will flood every time it rains. Look around your yard for spots where the grass seems to grow best, as these spots probably drain well. Ideally, your garden should be in a flat, even part of the yard. To find a spot that gets good drainage, wait until a few hours after a heavy rain and then go look around your yard for places where water is pooling. Avoid placing your garden in these spaces.

Summary:
Choose a spot for the garden that has good exposure to sunlight. Avoid root systems. Pick a spot with good drainage.