You've wisely resisted the urge to plant your warm-weather veggies in March. However, once the soil is dry enough to work, it's a good time to prepare the bed by incorporating plenty of organic material. Good items to add include Sweet Earth, Soil Builder, composted cow or chicken manure, and compost. We like to add more than one kind of material--the more the better!
Once the danger of frost has passed, which is around April 20 in our area, it's time to start planting.
It's important to know which vegetables to plant as seeds, and which to plant as starter plants.
These plants can be installed as seeds: string beans, corn, lima beans, zucchini, yellow squash, pumpkins, and watermelons. Onions should be planted as sets, a.k.a. bulbs. Be sure to read the seed packet instructions as to depth to plant, distance between rows, and germination time.
These plants can be put in as starter plants: strawberries, any type of squash, watermelon, tomatoes, and peppers. Notice that squash is listed in both the seed and plant categories. Either way works. It just depends on how patient you are! Please know that it is especially important to wait to plant tomatoes and peppers until the soil is warm. That can easily be in May. Don't rush it. If you do plant while the soil is cold and too damp, your tomato and pepper plants will just sit there, and possibly rot rather than grow.