If you want to make a garden out of scratch, there are just a few things to keep in mind.
First: you can do it! Plants often grow in spite of humans and so there is no way that this is a bad idea. Depending on what you want to grow, there may be specific requirements like pH, light/shade, fertilizer, or space.
A vegetable garden can vary in size from a pot to a farmers field. I find that a square the size of a piano will produce enough weeds to keep most people pulling without giving up. Any size, it is important to assess the existing soil where the garden will be made. If you are planning to grow in what use to be grass, there is probably already decent soil underneath. The sod will need to be removed so that you can see the quality of the soil.
Any earth to be used for growing needs to be of high quality. If you are lucky enough to have good black dirt there is little to do but spade it or roto-till it as prep for planting. More than likely, there will need to be black dirt added to your location. If the soil is rocky, sandy, or otherwise not black, you can buy soil at your garden center for a reasonable price.
Location is something to think long and hard about. Proximity to water and a place where you can see the garden to enjoy are important but there are a few bad locations. Walnut trees contain a toxin (the tannins that were used by Native Americans to tan hides) will keep plants from growing. Anywhere under the drip zone (under the canopy) of a walnut tree is an impossible place for a garden. The shade of any other tree can be a benefit or harmful if it blocks too much of the suns light. Depending on what plants you plan to grow, some natural shade can be beneficial.
Adding manure or other fertilizer may be required if the soil is less than good black dirt. Warning: adding “hot” or fresh manure can damage your garden. If you are getting manure for fertilizer straight from the farm, try and get some that is a year old. Too hot of fertilizer can ‘burn’ the plants.
Soil should be made as less clumpy as possible. Seed to soil contact is necessary for sprouting and clumps minimizes this contact. A spade can be used to crush or cut up clumpy soil. There are also motorized roto-tiller machines that do this with ease.
With luck, your well thought out garden can produce for many years.