Watermelons demand warm temperatures to grow. The seeds need a temperature of 75 degrees Fahrenheit. So it is better to start the seeds indoors and then transfer the watermelon vines outside in the ground when they are 6-8 inches long. You can also buy transplants from the nursery if you do not want to grow right from the seed.
Get watermelon seeds from your local seed shop or nursery. You have to get both diploid (seeded) and triploid (seedless) seeds because the seedless watermelons are sterile and cannot pollinate. They need a seeded watermelon to pollinate and grow a fruit.
Dig holes on the ground where you want to grow the watermelons. Now sow one seeded watermelon in the first hole. Sow seedless watermelons in the next two holes. Follow this pattern for all the seeds; one seeded and then two seedless. Cover the seeds with 3-4 inches of soil so that they can germinate well. Press the soil down a bit so that the seeds are in contact with it. You should remember the sowing pattern so that you can distinguish your seedless watermelons.
Water the seeds regularly as the melons need a lot of it for the juice. Make sure that you follow a particular schedule for watering and taking care of the watermelons. You will be able to enjoy the fruits within a couple of months. Do remember that you will also get regular watermelons in this way, though their quantity will be half of the seedless ones.