Flower or vegetable, large seed or small, certain fundamentals are universal to starting seeds that will later be transplanted. During the germination phase, the seeds must be kept constantly moist. Once the nurse leaves have broken ground, the young plants need light and air circulation. As the young plants develop, they need the right amount of room for root growth. Keep these fundamentals in mind and you can start most anything successfully.
Pour a couple of gallons of sterile, soil-less seed-starting medium into a plastic tub. Add water and mix by hand until the entire quantity of starting medium is moist. You want the starting medium moistened to the point that it will form a ball when you squeeze some in your palm, but the ball will fall apart when pressed with a finger tip. If the medium won't form a ball, add more water. If the ball holds together when you poke it, add more medium.
Fill a germination tray with the moistened starting medium. A germination tray is typically 11 inches wide by 20 inches long by 1 inch deep with drainage slots distributed evenly over the bottom. They are designed to fit in a drip tray, which will allow excess water to drain away from the germination tray.
Sow your seeds in the starting medium. A rule of thumb for planting depth is that the seed should be planted at a depth equal to the seed's largest dimension. For example, tiny lettuce seeds should be sown on the surface and then simply pressed into the surface with your palm. Tomato and pepper seeds that are about one-quarter-inch diameter should be planted about one-quarter-inch deep. Sow more seeds than you need plants to set out.
Place the germination tray in the drip tray and cover with the clear tray dome or with plastic food wrap. Covering the tray will retain moisture in the thin tray.
Place the tray in a warm location. There are specialized heaters you can buy that are designed to fit one or two flats. The top of a refrigerator works nearly as well and costs nothing.
Mist the starting medium with the spray bottle daily. The medium should be always moist, but never soggy.
Remove the dome or plastic wrap once the first seedlings break the surface and place the tray under a fluorescent light fixture. A south-facing window can substitute, but plants will develop long, spindly stems and bend toward the window. Adjust so that the light fixture is about an inch above the seedlings. Without the cover, it becomes critical to monitor the moisture of the medium and keep it misted.
Transplant the seedlings from the germination tray into a cell flat when the plants have one or two sets of true leaves (those appearing after the cotyledons or "nurse" leaves). The cell size of the flat should match the size you want the plants to be when you set them out. Cells of 3.5 inches by 3.5 inches are appropriate for peppers, tomatoes and eggplant, for example.
Fertilize the plants with half-strength liquid fertilizer.
Set the flats outside whenever the temperature is above the mid-40s F and the wind is gentle. This approach will produce stronger plants than keeping them inside until just before time to set them out. Sunlight, gentle winds and cool but not cold temperatures produce robust, vigorous plants.