The beds should be narrow enough so the center can be reached from the walkways. A three feet wide bed with a one foot wide walkway works well. The soil can be mounded with a lower walkway inbetween. Even better, surround the soil with pressure treated 2X12's. The preservative used doesn't affect plants roots like the creosote in railroad ties.
Seed Be sure to use fresh seed from a reputable company.
Some seeds have very particular requirements to grow, so read and follow the directions carefully. For example, carrot seeds must be planted shallow enough that they will receive orange light in order to grow. Many seeds require that the soil be above a certain temperature. Seeds that require warm soil and a long growing season, such as tomatoes, peppers and squash, are usually started indoors and transplanted outdoors when the soil is warm. Use a special seed starting mix and peat pots and start the seeds about 6 weeks before they are to be planted outdoors.