To make a good garden you must have good soil.
Once you've decided which vegetables you want to plant and where, there is still a little bit of preparation to complete before planting.
All vegetables get water and nutrients from the soil. In some cases, the ground won't already have the needed compounds. In others, previous plantings over many years will have depleted them. Either circumstance can easily be remedied with a few simple actions.
First, know what you're starting with. The best way to find out is to purchase an inexpensive soil testing kit. These easy-to-perform chemical tests will provide accurate information on nutrient levels, pH and other helpful data. For more accurate tests, you can seek out the local Extension Office of a university. They often work with local planters to provide information about the environment, including soil composition.
pH levels can be adjusted with the addition of small amounts of sulfur or lime. Some plants prefer earth that is slightly alkaline (basic), others do better in slightly acidic soil. A garden underneath a pine tree, for example, will tend to be slightly acidic because the needles that fall give a small amount of acid to the dirt. A medium level is best for most vegetables, with a pH between 6.0-6.5.
There is some mechanical preparation to be done as well. Depending on the soil type you have - very clay like, sandy, sandy loam or a mixture - you may need to do more or less tilling. Rototillers can be rented. If you have a large area that you'll replant year after year it may be worthwhile to endure the one time expense and buy one, however. You'll use it more often than you suspect.
The soil needs to be aerated and turned to provide oxygen and the right mechanical support balanced with the right degree of freedom for the roots to spread. Very compact soil makes it difficult for nutrients and water to flow and drain. It keeps roots from moving down to reach lower water levels and provide stronger support against wind.
Any weeds present should be dealt with at this time. The more you do now, the less you need to do later. Many won't appear but will have seeds present ready to sprout after you plant. A soil preparation mixture that prevents weeds from starting is a good idea. It's much easier to apply before you plant your vegetables and it won't harm them once you do. They're designed to kill weeds, but not other plants.
You might want to lay down a weed control fabric before planting. That creates a cover that makes it more difficult for weeds to develop, by denying them sunlight. It also provides a physical barrier that makes it harder for them to rise up.
Now is also a good time to attack insects, bacteria and other things that will eat your vegetable plants later. Some organisms are helpful. Milky spores, for example, are bacteria that interrupt the growth cycle of the Japanese beetle larvae. As they develop they eat roots. Laying down the appropriate mixture of pesticides can be safe and effective and will cover a wide range of potentials pests. Preventing a small problem is always easier than solving a larger one later.
Preparing the soil before planting will pay off many times over later. The savings in effort, time and money will help produce the best vegetables possible from your garden.