The depth you plant your seeds depends on their size. They only need enough soil to cover them and supply moisture for germination. Seeds buried too deep may not be able to struggle through the soil to the surface. As a rule of thumb, seeds should be covered up to twice their diameter at their largest point. After you've set the seeds at the correct depth, firm the soil by tamping it with your hands or the end of your garden rake. This will improve contact between the seeds and the moist soil.
Seed spacing is also critical: If plants are forced to grow too close together, they may produce little or no yield. If seeds are large enough to handle, such as beans and corn, it's fairly easy to space them correctly. But with tiny seeds, spacing can be tricky. Take your time in spacing while planting, but you'll still probably have to thin seedlings soon after germination.
Decide whether you'll sow seeds in a single row or a wide row. Vegetables such as beets, carrots, collards, kale, leaf lettuce, mustard, radishes, and spinach will produce nicely in wide rows while conserving space and water. The rows should be no wider than about 36 inches, making it easy to maintain and harvest vegetables. Prepare the row by loosely raking the soil, leaving the indentations made by the rake. Sprinkle the seeds evenly over the soil, and use the rake to press them into the soil. Cover the row with a thin layer of soil, straw, or loose compost to help keep the soil moist.
Planting in a single row is the most commonly used seeding arrangement. It's the easiest to maintain because you can comfortably cultivate between rows, but it's the least economical. Plants dry out faster, and there is more unused garden space.
Plants such as cucumbers and squash and other trailing vegetables benefit from planting in inverted hills: a shallow depression made by removing an inch of soil from a circle about a foot across and using the soil you've removed to form a rim around the circle. The inverted hill catches and holds extra moisture. During a heavy rain the outer rim of the soil, instead of being washed away, falls in toward the plants, providing extra anchorage for shallow-rooted plants.