The soil conditioning is largely dependent on how large your garden will be. So before I go into what's important, make sure you have an idea of how big your garden will be. If you are doing a relatively small garden (4×4 feet- 10×10 feet) you won't have to worry about drainage, or turning the soil every season. For example, if you are doing a raised bed garden you won't have to till up the grass in your yard to do so, you can just build the bed and fill it with dirt & compost. The compost is a great medium for plants to grow in and does not require extra work to get great results, also it will drain just fine on its own.
With larger gardens (10×20 feet- 1 acre or more) the ability to just fill it in with compost becomes very expensive, time consuming, and can still have flooding that will kill your plants. With a larger garden tilling up the grass or dirt is the first step. The ground needs to be broken up, once its broken up it can be planted in. Many people use a tiller or a disc to break up the ground but depending on the size, you can easily rent equipment or invest in buying some equipment to prepare the soil each year. Once you have turned the soil a bit and have it broken down to small chunks smaller than your fist and at least 5 inches deep you should focus on preparing for drainage. Take a step back and look for low spots in the landscape and either make a small ditch or buy drainage pipe to put in the ground before you get all the plants in the ground. This is a CRITICAL step, do not overlook it or ignore it, one hard rain could kill half of your garden in a matter of a day or two and there will be nothing you can do (yes its happened to me). Since the ground is tilled up and loose digging a drainage ditch or putting in plastic piping is very easy. Depending on the size you may need just a shovel and a couple hours or you may need heavy equipment to dig the ditch.
As I said before, planning for all of this can be the difference between success or failure. Taking a few hours to take a step back, look at what you want to do and where, and then seeing it before its there is a powerful way to become successful the first time rather then suffer through trial and error.